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Investigation of the direct current determination of electrolytic conductivity : measurement of strain… McFadden, William Hamilton 1951

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I . INVESTIGATION OF THE DIRECT CURRENT DETERMINATION  OF ELECTROLYTIC CONDUCTIVITY  I I . MEASUREMENT OF STRAIN POTENTIALS by WILLIAM HAMILTON McFADDEN A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Chemistry We accept t h i s t h e s i s as conforming t o the standard r e q u i r e d  from-candidates f o r t h e  degree o f MASTER OF ARTS..  Members o f the Department o f Chemistry.  THE UNIVERSITY OF BRITISH COLUMBIA April, 1 9 5 1 .  ABSTRACT - p a r t i  The c e l l constant of a d i r e c t c u r r e n t c o n d u c t i v i t y c e l l was measured u s i n g as a standard 0.1M potassium  and O.OLM  c h l o r i d e s o l u t i o n s and s p e c i f i c c o n d u c t i v i t y  23 d a t a o b t a i n e d by G, Jones and M. Prendergast.  The r e s u l t s  obtained f o r e i t h e r o f the s o l u t i o n s were exact t o w i t h i n one o r two p a r t s i n t e n thousand, but a d i f f e r e n c e of 0.6f  0  e x i s t e d between the two c e l l constant v a l u e s . I n order t o i n v e s t i g a t e more e x a c t l y the nature o f t h i s v a r i a t i o n , o t h e r c o n c e n t r a t i o n s were measured u s i n g as a standard the d a t a obtained by T. Shedlovsky, A.S. Brown, and D.A. Maclnness? C e r t a i n f a c t o r s i n t h e design of a d i r e c t c u r r e n t c e l l have been considered and suggestions f o r f u t u r e work offered.  ABSTRACT - p a r t I I  S t u d i e s have been made o f the anodic p r o p e r t i e s of s t r a i n e d copper w i r e i n t h e Cu ( s t r a i n e d ) Two  cell  CuS0  4  Cu (normal),  copper w i r e s were immersed i n copper s u l p h a t e s o l u t i o n .  Weights were added t o one of these and the p o t e n t i a l  dif-  f e r e n c e measured p o t e . n t i o m e t r i c a l l y o r w i t h a vacuum tube v o l t - m e t e r . The r e s u l t s obtained show t h a t (1) the r e l a x a t i o n of tBais p o t e n t i a l i s approximately exponential, ( 2 ) v e r y l i t t l e p o t e n t i a l i s developed u n t i l a c r i t i c . a l strain i s applied, ( 3 ) a f t e r a c e r t a i n s t r a i n has been a p p l i e d the peak p o t e n t i a l developed becomes constant w i t h i n c r e a s ing s t r a i n , (4) the magnitude of the e f f e c t i s dependant on the c o n c e n t r a t i o n of the s o l u t i o n , (5) t h e magnitude and d i r e c t i o n (anodic or c a t h o d i c ) of the p o t e n t i a l i s dependant upon the components of the e l e c t r o l y t e .  ACKNOWLEDGEMENT  The  work presented  here, has been performed under t h e  s u p e r v i s i o n of Dr. L.W. S h e m i l t . The author would l i k e t o thank him f o r the suggestions,  criticisms,  ment g i v e n d u r i n g t h e course o f t h i s The  and encourage-  research.  author i s a l s o g r a t e f u l t o Mr. R.S. Dudley f o r  the a s s i s t a n c e r e c e i v e d i n t h e study o f s t r a i n p o t e n t i a l s . An  acknowledgement i s a l s o made t o t h e N a t i o n a l Research  C o u n c i l f o r f i n a n c i a l a i d r e c e i v e d d u r i n g t h e months May  and June, 1950.  CONTENTS Part I . INVESTIGATION OF THE DIRECT CURRENT DETERMINATION OF ELECTROLYTIC  I  II  III IV  CONDUCTIVITY  Introduction  page 1  History  2  Theory  4  E x p e r i m e n t a l Methods and R e s u l t s  10  D e s c r i p t i o n of Apparatus  10  E x p e r i m e n t a l Procedure  13  Experimental Results  21  D i s c u s s i o n of R e s u l t s  24  Bibliography  28  Part I I . MEASUREMENT OF STRAIN POTENTIALS  I  Introduction  31  History  31  Theory  33  II  E x p e r i m e n t a l Techniques and R e s u l t s  III IV  page 35  D e s c r i p t i o n o f Apparatus and E x p e r i m e n t a l Procedure  35  Experimental Results  37 ' 42  D i s c u s s i o n of R e s u l t s  45  Bibliography  TABLES Table 1.  Accuracy Obtainable i n R e s i s t a n c e Measurement.  21  C e l l Constant V a l u e s Using 0 . 1 and 0 . 0 1 Demal S o l u t i o n s .  22  Table  2.  Table  3.  C e l l Constant V a l u e s at V a r i o u s C o n c e n t r a t i o n s . 23  Table  4.  E l e c t r o d e P o t e n t i a l versus Time.  38  Table  5.  Peak P o t e n t i a l versus S t r a i n .  39  Table  6.  E f f e c t of C o n c e n t r a t i o n on E l e c t r o d e Potential.  40  Table  7.  E f f e c t of D i f f e r e n t E l e c t r o l y t e s on Electrode Potential.  41  ILLUSTRATIONS  Mechanism of R e l a x a t i o n F o r c e .  F i g u r e 2.  Conductance C e l l .  Figure 3a. 3b.  Prohe E l e c t r o d e s used by Gordon. on page i i " " " i n t h i s Reasearch. 11  F i g u r e 4.  Thermoregulator  F i g u r e 5*  Current R e g u l a t o r and Measuring  F i g u r e 6.  on page  6  F i g u r e 1.  f o l l o w i n g page 10  Relay C i r c u i t ,  f o l l o w i n g page 12  Complete Circuit.  F i g u r e 8. Figure 9.  "  12  "  "  23  "  "  36  "  "  38  " C e l l Constant" versus S p e c i f i c Conductivity.  Figure 7.  "  Electronic Millivoltmeter Circuit. Negative Change i n E l e c t r o d e P o t e n t i a l versus Time. Peak P o t e n t i a l v e r s u s S t r a i n i n g Load.  F i g u r e 10. Negative Change i n E l e c t r o d e Potential f o r Various C o n c e n t r a t i o n s o f CuSO^-  " 3 9  "  "  "  40  F i g u r e 11. Negative Change i n E l e c t r o d e Potential f o r Various E l e c t r o l y t e s . "  "  41  P l a t e 1. The Conductance C e l l .  »  P l a t e 2. The S t r a i n P o t e n t i a l C e l l .  "  " 1 0 »  35  INVESTIGATION OF THE DIRECT CURRENT DETERMINATION OF ELECTROLYTIC CONDUCTIVITY  I . INTRODUCTION In a c o n s i d e r a t i o n o f t h e e l e c t r o l y t i c  properties  o f s o l u t i o n s , one o f the most fundamental types of experimental  evidence has been t h a t of c o n d u c t i v i t y . Modern  t h e o r i e s of s o l u t i o n s o f e l e c t r o l y t e s , most n o t a b l y the Debye-Huckel t h e o r y f o r e be considered  of i n t e r i o n i c a t t r a c t i o n , must  there-  i n the l i g h t of experimental conduc-  tance measurements. The main emphasis t o date has been i n the e x p l o r a t i o n of v e r y d i l u t e s o l u t i o n s where  theore-  t i c a l c a l c u l a t i o n s from modern t h e o r i e s are p o s s i b l e . An insight regarding electrolyte,  the e f f e c t s o f c o n c e n t r a t i o n ,  and type of s o l v e n t  In t h i s regard,  type of  i s g r a d u a l l y being made.  s i n c e most measurements have been made  u s i n g HgO as a s o l v e n t , one o f the more i n t e r e s t i n g possi b i l i t i e s i s a study o f s o l u t i o n s i n DgO,  a solvent with  the same chemical p r o p e r t i e s as H 2 O but w i t h many d i f f e r ent p h y s i c a l p r o p e r t i e s . T h i s r e s e a r c h has t h e r e f o r e been planned t o develop a d i r e c t c u r r e n t method o f  conductiv-  i t y measurement, and apply i t t o the measurement of potassium c h l o r i d e s o l u t i o n s i n Dg©* The success obtained  to  date w i t h the development and t e s t i n g o f a d i r e c t current method f o r c o n d u c t i v i t y measurement i s r e p o r t e d thesis.  i n this  - 2 -  HISTORY In 1888,  a comparison between a l t e r n a t i o n and  c u r r e n t methods of measuring c o n d u c t i v i t y was S h e l d o n . The  direct  made by  i r r e p r o d u c i . b i l i t y of a r e s i s t a n c e measurement  1  u s i n g d i r e c t current was  shown to be due  to the p o l a r i z a -  t i o n produced at the e l e c t r o d e s . Thus today, although some r e s e a r c h has  been done by d i r e c t c u r r e n t methods, most  e x i s t i n g conductance data have been obtained a l t e r n a t i n g current The tance was  f i r s t r e s e a r c h paper on d i r e c t current 2 published  ured  two  by E. Newbery  i n 1918,  conduc-  Using  a  cell  a c t i n g as c u r r e n t c a r r -  as probes to measure a v o l t a g e drop, he meas-  the c o n d u c t i v i t y of s e v e r a l concentrated e l e c t r o l y t e s  but obtained  agreement w i t h the e x i s t i n g a l t e r n a t i n g cur-  r e n t data o n l y w i t h i n s i x t e n t h s o f one l a t e r , E.D.  Eastman^ used a modified  a l t e r n a t i n g and of a one  percent. Two  d i r e c t c u r r e n t to measure the c o n d u c t i v i t y  normal potassium c h l o r i d e s o l u t i o n . He  a l t e r n a t i n g and  years  bridge adapted to both  a d i f f e r e n c e of about seven p a r t s i n one d i r e c t c u r r e n t values  observed  hundred between  but t h i s d i f f e r e n c e  can  be a t t r i b u t e d to the e f f e c t s of p o l a r i z a t i o n t h a t  not  been f u l l y  Noyes J r .  had  e l i m i n a t e d . Another approach to d i r e c t  c u r r e n t measurement was W.A.  an  source.  w i t h f o u r calomel e l e c t r o d e s , two i e r s and  by u s i n g  The  made i n 1921  by C. Marie and .  e f f e c t of p o l a r i z a t i o n was  partially  removed by u s i n g hydrogen e l e c t r o d e s on p l a t i n i z e d  platinum  - 3 -  and measuring the r e s i s t a n c e d i r e c t l y . However, the obtained d e v i a t e d about one I n 1935,  J.N.  tt Bronsted  results  percent from Kohlrausch's  and R.F.  Nielsen  5  data.  used t h i s method to  measure^ s o l u t i o n s of h y d r o c h l o r i c a c i d at c o n c e n t r a t i o n s as low as 0.002N. Although  the e f f e c t s of p o l a r i z a t i o n were f u r -  t h e r e l i m i n a t e d by c l o s i n g the c i r c u i t f o r l e s s than one- . h a l f of a second, the r e s u l t s v a r i e d about f i f t e e n one-hundr e d t h s o f one percent from the best e x i s t i n g c u r r e n t d a t a . Another method was  alternating  used by L.V.  Andrews and  6 W.E.  Martin  t o study the conductance of potassium c h l o r i d e  s o l u t i o n s down to 0.0005N; t h e i r technique,  however, i s open to  c r i t i c i s m and t h e i r r e s u l t s are of d o u b t f u l accuracy i n g to modern standards. The  accord-  best c o n d u c t i v i t y values  obtained by a d i r e c t c u r r e n t method are those r e p o r t e d by 7 A.R.  Gordon' and h i s c o l l a b o r a t o r s s i n c e 1941.  By r e d e s i g n i n g  the c e l l used by Newbery, and r e p l a c i n g the calomel e l e c t r o d e s by s i l v e r - s i l v e r c h l o r i d e e l e c t r o d e s , c o n d u c t i v i t y values have been r e p o r t e d f o r s e v e r a l e l e c t r o l y t e s at v a r i o u s temperatures  agreeing w i t h i n two  or t h r e e one-hundreths of a  percent w i t h the best a l t e r n a t i n g c u r r e n t data. Another d i r e c t c u r r e n t d e t e r m i n a t i o n of potassium has,been made r e c e n t l y by R.F.  chloride solutions  Palmer and A.B.  Scott  but  s e v e r a l p r e c a u t i o n s were overlooked and •tBaeir r e s u l t s are not as accurate as those r e p o r t e d by Gordon.  - 4 -  THEORY  tt The Debye-Huckel  Theory.  In the e a r l y c o n s i d e r a t i o n s o f the t h e o r y o f s o l u t i o n s of e l e c t r o l y t e s t h e decrease o f e q u i v a l e n t conductance as the c o n c e n t r a t i o n i n c r e a s e d was a t t r i b u t e d t o a d e c r e a s i n g number o f i o n s . T h i s t h e o r y l e d t o the e q u a t i o n used f o r the degree o f d i s s o c i a t i o n proposed by A r r h e n i u s which i s  A . i n which and  <==< i s the c l a s s i c a l degree o f d i s s o c i a t i o n and A c  / \ are r e s p e c t i v e l y the e q u i v a l e n t conductance at con0  c e n t r a t i o n " c " and a t i n f i n i t e d i l u t i o n . Although t h i s  equ-  a t i o n h e l d w e l l f o r weak e l e c t r o l y t e s , i t could not be used w i t h data obtained f o r s t r o n g e l e c t r o l y t e s , and so i t became evident t o many observers t h a t a new t h e o r y should be proposed. The s u c c e s s f u l i n t r o d u c t i o n o f such a t h e o r y was due "  9  to P. Debye and E. Huckel  who i n t e r p r e t e d  electrolytic  phenomena by c o n s i d e r i n g the p r o p e r t i e s tobe due t o an i n t e r p l a y o f the thermal f o r c e s and the coulombic f o r c e s e x i s t i n g i n t h e . e l e c t r o l y t e . They a p p l i e d c e r t a i n fundamenta l s o f e l e c t r o s t a t i c s and s t a t i s t i c a l mechanics t o the e l e c t r o l y t i c system and by making s u i t a b l e approximations a r r i v e d at proper mathematical e x p r e s s i o n s . The I o n i c Atmosphere.  I t was shown by Debye and H&cEcel  that a s t a t i s t i c a l charge d i s t r i b u t i o n o f o p p o s i t e s i g n , c a l l e d the i o n i c atmosphere,  e x i s t e d around any g i v e n i o n i n  a s o l u t i o n . T h i s i o n i c atmosphere  i s c e n t r a l l y symmetrical  - 5 -  a n d  i t s  i o n  t o  p r e s e n c e be  c a u s e s  l o w e r e d  b y  t h e  a n  p o t e n t i a l  a m o u n t  g i v e n  d u e b y  t o  t h e  c o n s i d e r e d  t h e  e x p r e s s i o n  i o n i c  a t m o s p h e r e ,  D w h e r e i s  i s  t h e  a n t  t h e  p o t e n t i a l  e l e c t r o n i c  o f  t h e  u n i t  s o l v e n t  D e b y e - H t l c k e l  t o  c h a r g e ,  a n d  t h e o r y  d u e  i s  ^  ,  t h e  " D "  a n  d e f i n e d  i s  t h e  d i e l e c t r i c  i m p o r t a n t b y  !% TT 7 7  t h e  q u a n t i t y  £  c o n s t i n  t h e  e q u a t i o n  €  y DAT .in  w h i c h  v o l u m e , u t e  " n " " k "  a n d  d i s t a n c e  a t  i s  J^-  t h e  w i t h  l i m i t i n g m u s t  w i l l  p e n d s T h i s  t o  D e b y e  w h i c h  i o n i c  t h e  a n  t h e  t h e  a p p l i e d a  w h i c h  o f  m e d i u m .  c a l c u l a t e d  / \  b y  a  i s  t h e  a n  H o w e v e r , s o  p e r  u n i t  p o t e n t i a l  a n d  o n  a p p l y i n g  m a g n i t u d e  o f  t o  a n  t h i s  m o s t  L a w ,  a b s o l -  i s  d e n s e .  t h e  T h u s ,  a t m o s p h e r e .  s e l e c t e d  t h e  o n l y i o n i c  t h a t  e a c h  v o l u m e ,  t h e  i n c r e a s e  u n i t  0  p o t e n t i a l i o n o h  i n  D e b y e  r e s i s t a n c e .  w i l l t h e  a t m o s p h e r e e l e m e n t  w h i c h  t h e . e l e c t r i c a l  t e r m e d  S t o k e s '  t h e  e x t e r n a l a  a  r e c i p r o c a l  d e p e n d e n t  f o r c e  e q u i v a l e n t B y  W h e n  f o r c e ,  o f  i o n i c  i n  i s  "T"  i s  s o l u t i o n ,  .  Q  t h e  i s  k i n d  F a l k e n h a g e n " ) "  d i r e c t i o n ,  r e t a r d a t i o n  f o r c e ,  o f  w h i c h  o p p o s i t e o n  a n d  F o r c e .  c o n d u c t a n c e  a n d  a t m o s p h e r e  t h i c k n e s s  " v ^ "  e a c h  d i m e n s i o n s  e l e c t r o l y t i c  a c t e d  c a u s e s  t h e  t h e  v e l o c i t y  i n  be  o n  ^  o f  c o n s t a n t  a c c o r d i n g  i o n  m o v e  i o n s  t h e  t o a  o f  B o l t z m a n n  E l e c t r o p h o r e t i c  a p p l i e d  m o v e  n u m b e r  . h a s  c a l l e d  T h e  i t  i s  t h e  t e m p e r a t u r e .  l e n g t h ,  i s  i s  o f  d e d e n s i t y .  e l e c t r o p h o r e t i c t h e a n d  v i s c o s i t y H ' u o k e l  -  The  Relaxation Force.  6  -  Another mechanism t e n d i n g t o de-  crease the e q u i v a l e n t conductance o f an e l e c t r o l y t e i s the r e l a x a t i o n f o r c e . T h i s f o r c e a r i s e s from the f a c t t h a t when a c e n t r a l i o n moves, the i o n atmosphere moves w i t h i t , but. t h e r e i s a time l a g o r r e l a x a t i o n time i n v o l v e d which gives the u n i t an a s y m m i t r i c a l  form. T h i s i s i l l u s t r a t e d i n f i g u r e 1  where the c e n t r a l i o n , i n i t i a l l y at "a" has now moved t o "b", but the atmosphere has remained s t a t i o n a r y . The magnitude o f -8 t h i s time l a g i s o n l y o f the o r d e r o f 10  seconds, but i t i s  s u f f i c i e n t t o cause a n . e l e c t r o s t a t i c f o r c e , independent o f the v i s c o s i t y o f the medium, which opposes t h e motion o f the ion.  F»r-"RE-  The  1  d e r i v a t i o n o f the exact mathematical r e l a t i o n s h i p f o r  the r e l a x a t i o n f o r c e i s q u i t e e l a b o r a t e , but i t i s worthy to  note t h a t the a c t u a l v a l u e o f i t depends on  ~\ . a  The  Debye-Hupkel-Onsager E q u a t i o n .  The  l i n e a r r e l a t i o n s h i p between the e q u i v a l e n t  tance served  conduc-  and the square r o o t o f the c o n c e n t r a t i o n had been obi n the n i n e t e e n t h  century  t i c a l e x p l a n a t i o n was presented.  by Kohlrausch I n 1927,  but no theore-  L. O n s a g e r  11  equated  -  7  -  the v a r i o u s f o r c e s present i n a conducting e l e c t r o l y t e at at e q u i l i b r i u m based on the Debye-Huckel concept d e r i v e d the f o l l o w i n g e x p r e s s i o n f o r  ~\  0  and  thus  , the e q u i v a l e n t  i o n conductance.  i n which " z " and dielectric  " z " are the v a l e n c e s , "D"  are the  constant and v i s c o s i t y of the s o l v e n t , and"T" i s  the a b s o l u t e temperature.  Also  and I f we  and TJ  ^ fe +2r)fz X;+zXo) +  +  consider a uni-univalent e l e c t r o l y t e i n a given solvent  at a g i v e n temperature,  the Onsager equation reduces  to  X - X, -feX.' + a'JVc i n which'-0-  and  law of independent  are c o n s t a n t s . By a p p l y i n g Kohlrausch's m i g r a t i o n of i o n s , an equation f o r  can be o b t a i n e d . Thus,  A = A c - (V\ot^]Vc~ T h i s equation i s s i m i l a r to the one proposed f o r the conductance o f s t r o n g e l e c t r o l y t e s ,  by K o h l r a u s c h but i n the  Onsager equation the v a l u e of the c o n s t a n t s ' i s p r e d i c t e d and assigned an exact p h y s i c a l s i g n i f i c a n c e .  -  8  -  A verification of the validity of this equation i s only possible by making precise measurements at low concentrations. This has been successfully accomplished by many different i n -  12  vestigators  for different types of salts and i n almost a l l  cases the data obtained in the laboratory agree  with the  theory for dilute solutions. The Shedlovsky Equation. Because the approximations made in deriving the DebyeHuckel-Onsager equation limit i t s use.to dilute solutions, many additions to this equation have been proposed. The nature of these additions may be theoretical, semi-empi r i c a l or empi r i c a l . One of the more important extensions i s the semiempirical equation proposed by T. Shedlovsky -^. In order to 1  interpret the data obtained at higher concentrations Shedlovsky extended the Onsager equation by considering additional concentration terms. Thus for most strong electrolytes the data are adequately expressed by the equation A  + c^i/F  =  Ac  +  BC  / - -0-Vc where *?B i s an empirical constant. In some cases i t i s necM  essary to improve this equation by adding two more terms thus obtaining the equation  + BC+  - 9 -  Although the Shedlovsky  equation was d e r i v e d from  experimental data, the terms "BC", "DC", and " l o g C" a r e o f the form r e q u i r e d by c o n s i d e r a t i o n o f the approximations  made  by Debye and Huckel; hence t h e term " s e m i - e m p i r i c a l " . The L i m i t i n g Conductance. In the f o r e g o i n g d i s c u s s i o n , the constant as an important  appeared  f a c t o r i n t h e Onsager equation and so the  methods of o b t a i n i n g i t s v a l u e w i l l be c o n s i d e r e d . The f i r s t i s t h a t suggested  by K o h l r a u s c h , where the conductance data  are e x t r a p o l a t e d t o i n f i n i t e d i l u t i o n . T h i s method g e n e r a l l y g i v e s agreement withthe t h e o r e t i c a l Onsager s l o p e , but has the disadvantage  o f depending on t h e data obtained from v e r y  dil-  ute . s o l u t i o n s . Another method o f e x t r a p o l a t i o n depends on some e x t e n s i o n o f the Onsager equation, u s u a l l y the one p r o A.  posed by Shedlovsky.  I n t h i s case, the e x p r e s s i o n  -t- G'T/C"  |_  i s p l o t t e d a g a i n s t the c o n c e n t r a t i o n and the l i n e extended t o the zero a x i s . Because o f the s e m i - e m p i r i c a l nature o f the equation, t h i s method o f o b t a i n i n g /\. has g i v e n e x c e l l e n t 0  r e s u l t s . A t h i r d method o f o b t a i n i n g :/Vo i s r e a l i z e d i n ."' Kohlrausch*s  law o f independent  m o b i l i t y o f i o n s . Because the  l i m i t i n g conductance o f an i o n i s a p r o p e r t y o f the i o n cons t i t u e n t i t s e l f , we may w r i t e A . o i n g i o n conductances and the value o f  =  "X° t X~  0  .. The l i m i t -  can be obtained from'.transference data  A o i S  thus secured. T h i s method i s extens-  i v e l y used f o r c a l c u l a t i n g  A . o f o r weak e l e c t r o l y t e s .  -  10 -  I I . EXPERIMENTAL METHODS AND RESULTS DESCRIPTION OF APPARATUS The Cell The conductance c e l l used in this research (figure 2) is of pyrex glass and is similar to the cells used successf u l l y by Gordon and his collaborators. It was made considerably smaller for the limited supply of solvent (DgO) for which i t was intended. The total volume of the c e l l is 140 m i l l i l i t e r s . The center section is 3 centimeters in diameter and the probe electrodes, P and P*, are 8.5 centimeters apart. The tube T-^ was used to f i l l the c e l l , while the tube T can be 2  used to conveniently save valuable solvent. Before use, the c e l l was boiled with concentrated hydrochloric acid, rinsed with doubly d i s t i l l e d water, and thoroughly steamed out. After this treatment the c e l l showed an even wetting on its surface when rinsed. It was never allowed to dry, and when not in use was always f i l l e d with the best conductance water available. The Main Electrodes. The two main current-carrying electrodes (M and M ) are made of heavy platinum f o i l joined to T  the copper leads by means of platinum wire which is fused into a soda glass rod. The platinum surfaces were silver plated and dipper into fused silver chloride with techniques described later. The Probe Electrodes. If probe electrodes are to serve as a means of measuring potential difference i t is necessary that their width, with respect to the path of the current,  to follow page 10  PLATE 1  THE CONDUCTANCE CELL .  to f o l l o w page 10  - 11 -  be s m a l l or there w i l l e x i s t a s e n s i b l e ohmic drop a c r o s s t h e i r s u r f a c e . The  e l e c t r o d e s used as probes by Gordon  ( f i g u r e 3&) adhere to t h i s requirement, found  but i t has  been  i n t h i s l a b o r a t o r y t h a t a s a t i s f a c t o r y s e a l of the  platinum d i s c to the g l a s s i s not e a s i l y o b t a i n e d . The ant contamination  result-  of the mercury contact r e s u l t s i n extraneous 14  p o t e n t i a l s which i n v a l i d a t e any p o t e n t i a l measurement.  The  probe e l e c t r o d e s used i n t h i s r esearch are shown i n f i g u r e 3 b . Platinum w i r e  (diameter  soda g l a s s and  0.081  centimeters) was  caged t o prevent  sealed into  any mechanical d i s t u r b a n c e  on  t h e a c t i v e s u r f a c e which would e f f e c t the p o t e n t i a l of the 15 electrodes.  These w i r e s were made i n t o s i l v e r - s i l v e r c h l o r i d e  e l e c t r o d e s a c c o r d i n g to the method of A.S.  FlCiURE  3  a  Fi G u The  Thermostat.  The  thermostat  46 cm.  x 28 cm.  R  Brown ^ 1  F  3b  consisted of a rectangular v e s s e l  x 28 cm.  p l a c e d i n a l a r g e wooden frame and  i n s u l a t e d w i t h t h r e e i n c h e s o f sawdust. The v e s s e l was t o a constant  filled  l e v e l w i t h I m p e r i a l D. B. o i l 52 c i r c u l a t e d  by a f o u r vane p r o p e l l o r p l a c e d as c l o s e to the c e n t r e of  - 12 -  the  bath as p o s s i b l e . The h e a t i n g element was  a c o i l of  nichrome wire, 22 gauge, w i t h a r e s i s t a n c e o f f i f t y ohms wound around a c o o l i n g c o i l  c a r r y i n g a slow steady stream 17  of water. The mercury thermostat  was  c o n s t r u c t e d from  a c o i l o f pyrex g l a s s i n o r d e r to o b t a i n a l a r g e s u r f a c e to  volume r a t i o . A metal t o g l a s s s e a l was  o b v i a t e d by l u b -  r i c a t i n g the stopcock w i t h g r a p h i t e , the o t h e r e l e c t r i c a l c o n t a c t t a k i n g p l a c e i n a c a p i l l a r y . The r e l a y c i r c u i t c o n s t r u c t e d i n t h i s l a b o r a t o r y and i s shown i n f i g u r e 4. temperature was  was The  determined w i t h a Beckmann thermometer c a l -  i b r a t e d at 25 ± 0.002 degrees c e n t i g r a d e w i t h a platinum r e s i s t a n c e thermometer having an N.B.S. c e r t i f i c a t e . D u r i n g a run, the bath temperature d i d not v a r y by more t h a n 0.01  degrees and i t i s b e l i e v e d t h a t the v a r i a t i o n  w i t h i n the c e l l was The Measuring  considerably less. Circuit.  The r e s i s t a n c e of the c e l l was o b t a i n e d by measuring the v o l t a g e drop a c r o s s the probe e l e c t r o d e s and the v o l t a g e drop a c r o s s a 1000.0 ohm  s e r i e s r e s i s t a n c e c a l i b r a t e d by the  manufacturer. A Rubicon Potentiometer type B was  used i n con-  j u n c t i o n w i t h a Leeds and Northrup galvanometer type HS w i t h -11  a s e n s i t i v i t y o f 1 x 10  amps per m i l l i m e t e r s c a l e d e f l e c -  t i o n . The Weston standard c e l l used was  checked  periodically  w i t h two standard c e l l s kept f o r that purpose. An c u r r e n t r e g u l a t o r which was  electronic  a m o d i f i c a t i o n of the "constant 18  c u r r e n t " c i r c u i t o f D.J. Le.Roy and A.R.  Gordon,  gave s a t -  i s f a c t o r y r e s u l t s a f t e r a " b r e a k i n g i n " p e r i o d o f about 100 hours.  to follow page  12  i  110 D.C.  FIGURE 4  THERMOREGULATOR RELAY CIRCUIT,  FIGURE 5  CURRENT REGULATOR AND COMPLETE MEASURING CIRCUIT*  - 13 -  EXPERIMENTAL PROCEDURE. P u r i f i c a t i o n of M a t e r i a l s . Conductivity  Water.  The c o n d u c t i v i t y water was obtained  by r e d i s t i l l i n g d i s t i l l e d water from a l k a l i n e potassium permanganate s o l u t i o n i n a copper s t i l l .  I n t h i s apparatus the  steam passed through a s e r i e s o f b a f f l e p l a t e s where  traces  of spray were separated from the vapor. The vapor was then passed through a copper condenser where i t was f u l l y condensed  and c o l l e c t e d i n a f i v e l i t e r pyrex f l a s k f i t t e d w i t h a  pyrex siphon tube f o r withdrawing the water. The s p e c i f i c conductance  o f the water so obtained was 3 t o 3.5 x 1 0 ~ mhos. D  Potassium Argento Cyanide.  S i l v e r cyanide was p r e c i p -  i t a t e d by adding potassium cyanide s o l u t i o n 135 grams p e r l i t e r dropwise t o an a g i t a t e d n i t r a t e containing  containing solution of s i l v e r  315 grams per l i t e r maintained a t 0° cent-  i g r a d e i n an i c e bath. Bakers C P . potassiumx cyanide and Mallinkrodt  C P . s i l v e r n i t r a t e were used. The p r e c i p i t a t e  was washed twenty times w i t h c o n d u c t i v i t y water and d r i e d i n a vacuum d e s i c c a t o r .  I t was then b o i l e d w i t h an excess o f  19 potassium cyanide, f i l t e r i n g funnel,  f i l t e r e d through a pyrex s i n t e r e d  glass  and allowed t o c o o l . The p r e c i p i t a t e d  crys-  t a l s o f potassium argento cyanide were d r i e d and r e c r y s t a l l i z e d f o u r times by d i s s o l v i n g 50 grams o f the s a l t i n 100 m i l l i l i t e r s o f b o i l i n g c o n d u c t i v i t y water. The hot s o l u t i o n was f i l t e r e d and the r e s u l t i n g c r y s t a l s d r i e d i n a vacuum des.iccator  and s t o r e d  i n a brown g l a s s  b o t t l e . A l l glassware  used i n t h i s and o t h e r p u r i f i c a t i o n s was cleaned w i t h hot  - 14 -  chromic a c i d , washed t h o r o u g h l y w i t h wates, and f i l l e d w i t h d i s t i l l e d water when not i n use. S i l v e r Chloride. S i l v e r n i t r a t e solution containing 11.228 grams of the s a l t was added dropwise t o 500 of an a g i t a t e d s o l u t i o n c o n t a i n i n g  milliliters  5.233 grams of potassium  c h l o r i d e . The p r e c i p i t a t e d s i l v e r c h l o r i d e was p r o t e c t e d  from  decomposition by keeping the r e a c t i o n v e s s e l i n an i c e bath and by keeping i t covered w i t h r e d cellophane.  I t was washed  18 times w i t h d i s t i l l e d water, d r i e d i n a vacuum d e s i c c a t o r , and s t o r e d i n a brown g l a s s b o t t l e . Both s a l t s used had been r e c r y s t a l l i z e d twice by d i s s o l v i n g them i n c o n d u c t i v i t y water and f i l t e r i n g  through a pyrex s i n t e r e d g l a s i : f u n n e l .  Potassium C h l o r i d e . The Merck reagent grade c h l o r i d e used i n t h i s r e s e a r c h  potassium  t o prepare conductance  solutions  was r e c r y s t a l l i z e d three times by d i s s o l v i n g 450 grams o f the d r y s a l t i n a l i t e r o f c o n d u c t i v i t y water. I t was through a pyrex s i n t e r e d g l a s s f i l t e r i n g  filtered  f u n n e l each time and  d r i e d i n a c l e a n e l e c t r i c oven. A f t e r d r y i n g i t was s t o r e d i n c l e a n g l a s s stoppered product b o t t l e s s h i e l d e d from atmospheric samples  contamination by i n v e r t e d beakers. Two d i f f e r e n t o f the t h r i c e r e c r y s t a l l i z e d  s a l t were prepared but no  d i f f e r e n c e was observed between the conductance o f t h e i r solutions.  -  15  -  P r e p a r a t i o n of S i l v e r - S i l v e r C h l o r i d e E l e c t r o d e s . Main E l e c t r o d e s .  The p l a t i n u m s u r f a c e s of the main  e l e c t r o d e s were b o i l e d i n concentrated n i t r i c  acid  tforcughly r i n s e d i n c o n d u c t i v i t y water. The s i l v e r s o l u t i o n was  and plating  prepared by d i s s o l v i n g 10 grams of the potassium  argento cyanide i n one l i t e r of c o n d u c t i v i t y water. F r e e cyanide was  reduced t o a minimum by adding enough d i l u t e  silver  n i t r a t e t o produce a f a i n t c l o u d of s i l v e r c y a n i d e . The e l e c t r o d e s were supported i n the e l e c t r o l y t e , ained i n 125 m i l l i l i t e r i n t o holes d r i l l e d  cont-  e l e c t r o l y t i c beakers, by i n s e r t i n g  i n l u c i t e • c o v e r s . Platinum anodes were  used. The c a t h o l y t e was  g e n t l y s t i r r e d by pyrex g l a s s rods  d r i v e n by l i g h t s t i r r i n g motors and p r o t e c t e d from anode contamination by a s a l t b r i d g e c o n t a i n i n g the s i l v e r ing  plat-  solution. The two main e l e c t r o d e s of each c e l l were e l e c t r o l y s e d  i n s e r i e s f o r s i x hours at a c u r r e n t d e n s i t y of one amp  milli-  per square c e n t i m e t e r . A f t e r p l a t i n g , they were c a r e f u l l y  r i n s e d and kept i n c o n c e n t r a t e d ammonium hydroxide  (usually  o v e r n i g h t ) i n order t o remove excess cyanide. They were then t h o r o u g h l y r i n s e d w i t h c o n d u c t i v i t y water and the bottom h a l f of the p l a t e d f o i l was  dipped i n s i l v e r c h l o r i d e fused i n a  platinum c r u c i b l e . Probe E l e c t r o d e s .  The probe e l e c t r o d e s were cleaned i n  14 / hot chromic a c i d  (because t h e y had been flame annealed)  and  b o i l e d i n c o n d u c t i v i t y water f o r eight hours before p l a t i n g .  - 16 -  They were s i l v e r p l a t e d i n the same manner as the main e l e c t r o d e s at the same c u r r e n t d e n s i t y , but a f t e r s t a n d i n g i n ammonium hydroxide and r i n s i n g w i t h c o n d u c t i v i t y water, they were anodized i n 0,1 normal h y d r o c h l o r i c a c i d s o l u t i o n prepared from N i c h o l s C P ,  r e a g e n t . When f i r s t used e l e c t r o d e s  prepared i n t h i s manner may h i g h as 0.07  millivolts,  have a p o t e n t i a l d i f f e r e n c e as  but a f t e r continued use the p o t e n t i a l  d i f f e r e n c e i s seldom g r e a t e r than 0.015 s t a b l e throughout  m i l l i v o l t s and  quite  a single run.  When not i n use both the probe and main e l e c t r o d e s were kept i n c o n d u c t i v i t y  water.  P r e p a r a t i o n of S o l u t i o n s . Three balances were used f o r weighing i n t h i s r e s e a r c h , A l a r g e O e r t l i n g (London) balance w i t h a c a p a c i t y o f two grams and an average s e n s i t i v i t y of 0.3 m i l l i g r a m was  kilo-  s c a l e d i v i s i o n s per  used i n weighing water f o r the s o l u t i o n s , A  Henry Troemner ( P h i l a d e l p h i a ) a n a l y t i c a l balance w i t h an average s e n s i t i v i t y of 7 s c a l e d i v i s i o n s per -milligram was  used  t o weigh the potassium c h l o r i d e samples f o r 0.1 demal and 0.01  demal standard s o l u t i o n s . A l l weighings  on these two  balances were made by the t r a n s p o s i t i o n method, and were 21 c o r r e c t e d t o vacuum u s i n g handbook values of d e n s i t i e s . Potassium c h l o r i d e samples weighing l e s s than 0.7 were weighed on a Sartorious-Werke  (Gottingen)  grams  semi-micro  balance w i t h a s e n s i t i v i t y of t e n s c a l e d i v i s i o n s per  0.1  - 17 -  m i l l i g r a m s . The weights were c o r r e c t e d t o vacuum but were not t r a n s p o s e d . A l l weights used were c a r e f u l l y  calibrated  to the same b a s i s a g a i n s t a standard s e t of c l a s s S weights certified  by Voland and Sons, October 2 5 , 1943.  In p r a c t i c e a potassium c h l o r i d e sample was weighed t o the n e a r e s t t e n m i l l i g r a m s i n an a c c u r a t e l y t a r e d p l a t i n u m weighing boat. The sample was then dryed i n a vacuum d e s i c c a t o r at a p r e s s u r e l e s s than 0.1 m i l l i m e t e r s o f mercury and a temperature o f 100° c e n t i g r a d e f o r not l e s s than twelve hours. I t was cooled i n a c l e a n d r y desiiccator and weighed t o b e t t e r than one part i n t e n thousand. A f t e r weighing, the boat and sample were immediately t r a n s f e r r e d t o an a c c u r a t e l y t a r e d s o l u t i o n f l a s k and the r e q u i r e d s o l v e n t added to the n e a r e s t f i v e grams by measuring  i t i n a f i v e hundred  millilit-  er graduated f l a s k . The s o l u t i o n was weighed and any a d d i t i o n a l s o l v e n t was added by means o f a one m i l l i l i t e r  pipette.  The f i n a l weight o f s o l u t i o n , c o r r e c t e d f o r vacuum, was exact t o t e n m i l l i g r a m s o r one p a r t i n one hundred thousand. Where i t was n e c e s s a r y t o convert from mass t o volume c o n c e n t r a t i o n s , 22  the d a t a o f G.P. Baxter and C.C. Wallace  were employed.  A l l glassware used was cleaned w i t h hot chromic a c i d and t h o r o u g h l y r i n s e d w i t h b o i l i n g c o n d u c t i v i t y water. The s o l u t i o n f l a s k s were wiped w i t h "Kleenex T i s s u e s " before weighing. The platinum boats were cleaned by b o i l i n g f i r s t  i n concentrated  n i t r i c a c i d and then i n c o n d u c t i v i t y water, and were handled  - 18  -  w i t h tongs kept i n a d e s i c c a t o r and never used f o r o t h e r purposes. Before weighing a sample, the boats were wiped of  any potassium c h l o r i d e t h a t may  u s i n g l e n s paper manufactured  free  have adhered t o the o u t s i d e  by S c i e n t i f i c S u p p l i e s Company.  T r a n s f e r of S o l u t i o n s . The s o l u t i o n s were t r a n s f e r r e d from the weighing to  flask  the c e l l by a p p l y i n g a i r p r e s s u r e t o the s u r f a c e of the  l i q u i d and f o r c i n g the s o l u t i o n through a l o n g tube, w i t h a standard t a p e r , i n t o the f i l l i n g tube of the The a i r used was  fitted cell.  passed through concentrated potassium  hydroxide, concentrated s u l p h u r i c a c i d , and f i n a l l y c o n d u c t i v i t y water. T h i s method of t r a n s f e r  through  effectively  prevented any p o s s i b l e contamination from atmospheric fumes. Before each run, the c e l l six  and e l e c t r o d e s were r i n s e d  t o eight times w i t h the s o l u t i o n t o be measured. The  c e l l was  then f i l l e d and the e l e c t r o d e s which had been s t a n d i n g  i n a sample of the s o l u t i o n were p l a c e d i n p o s i t i o n . Because the  exact o r i e n t a t i o n of the e l e c t r o d e s i s c r i t i c a l , they  were a d j u s t e d t o the same p o s i t i o n each time by means of a f i n e l i n e on the male and female members of the t a p e r s . When f i l l e d w i t h s o l u t i o n the c e l l was the  immersed i n  thermostat, where i t a t t a i n e d thermal e q u i l i b r i u m w i t h i n  about twenty minutes, a f t e r which i t s r e s i s t a n c e c o n s t a n t . I t was the  shown t h a t r e f i l l i n g  the c e l l  remained  and r e p e a t i n g  measurement gave the same r e s i s t a n c e v a l u e , and so a  - 19 -  second measurement was f r e q u e n t l y omitted. Measurement o f R e s i s t a n c e . The was  c u r r e n t from t h e t h e r m i o n i c r e g u l a t o r ( f i g u r e 5)  passed  through  the c e l l  i n e i t h e r d i r e c t i o n by c l o s i n g  the r e v e r s i n g s w i t c h S-j_. With S-^ c l o s e d S5 connecting a 20,000 ohm p l a t e r e s i s t a n c e i n p a r a l l e l w i t h the c e l l was  opened t o a l l o w the f u l l  solution. S  2  c u r r e n t t o pass through t h e  and S-j a r e r e v e r s i n g switches t o the probes and  standard r e s i s t a n c e r e s p e c t i v e l y . When s e t i n t h e i r  proper  p o s i t i o n s , e i t h e r t h e v o l t a g e a c r o s s the probes o r a c r o s s the standard r e s i s t a n c e can be s e l e c t e d by changing  S.. I n  p r a c t i c e , t h e v o l t a g e a c r o s s the standard r e s i s t a n c e E measured then, without was  changing  s  was  the d i r e c t i o n o f the c u r r e n t ,  changed so t h a t t h e v o l t a g e across the probes E  be o b t a i n e d . The c u r r e n t was r e v e r s e d , E  g  could  and Ep again measur-  ed, and t h e average v a l u e s r e c o r d e d . The c u r r e n t through t h e c e l l was v a r i e d from 0.14 t o 0.29 m i l l i a m p s by changing t h e n e g a t i v e g r i d p o t e n t i a l from one and one-half v o l t s t o 6 v o l t s by means of a s e l e c t o r s w i t c h S • g F o r t h e g i v e n c u r r e n t , t h e value o f t h e r e s i s t a n c e o f the s o l u t i o n between t h e probes was c a l c u l a t e d from the formula, _Ep ^ ( o ohms being the v a l u e o f E the standard r e s i s t a n c e . ) The r e s u l t s obtained i n d i c a t e t h a t R  =  1  0  0  0  >  0  1  0  0  0  <  s  for  a g i v e n s o l u t i o n the r e s i s t a n c e measurement was independ-  ent of t h e c u r r e n t and e a s i l y reproduced  t o w i t h i n 0.02%.  -  2 0  -  S o l v e n t Conductance. The  s o l v e n t conductance was measured f o r each s o l u t i o n  immediately  p r e c e d i n g ^ the measurement on the s o l u t i o n . When  measuring such a h i g h r e s i s t a n c e t h e v o l t a g e a c r o s s the probes exceeds t h e l i m i t s of t h e potentiometer,  n e c e s s i t a t i n g meas-  urement by some other h i g h impedance instrument  or method.  One method used i n t h i s r e s e a r c h made use of c a l i b r a t e d  gal-  vanometer i n s e r i e s w i t h a 2 0 megohm r e s i s t a n c e . By knowing the c h a r a c t e r i s t i c s o f the galvanometer, one could c a l c u l a t e the c u r r e n t through  the r e s i s t o r and hence o b t a i n t h e t r u e  v o l t a g e across t h e probes. Another method simply measured the v o l t a g e w i t h a c a l i b r a t e d vacuum tube v o l t m e t e r . The r e s u l t s obtained by both methods agreed w i t h i n one percent, which i s t h e l i m i t of a c c u r a c y p o s s i b l e by e i t h e r method.  - 21 -  EXPERIMENTAL RESULTS I t was p r e v i o u s l y mentioned that a r e s i s t a n c e measurement was independent of the c u r r e n t . T h i s f a c t i s i l l u s t r a t e d by Table 1 showing a t y p i c a l s e t o f r e s u l t s obtained on a 0,02 N potassium c h l o r i d e s o l u t i o n at 25° c e n t i g r a d e .  TABLE 1. Es ' Es ' Ep Current ' Es ' Ep Ep • Mamps. ' V o l t s ' V o l t s ' V o l t s ' V o l t s ' V o l t s ' V o l t s ' 1  1  R Ohms  ' P o s . l ' Pos.2 ' Average' P o s . l ' Pos.2 'Average' 0.29  '0.30417' 0.30416' 0.30416' 0.14332' 0.14324' 0,14328' 473.07 r0.30420' 0.30420' 0 . 3 0 4 2 0 ' 0.14330' 0.14330' 0.14330' 471.07  0.24  '0.25380' 0.25380 0.25380' 0.11958' 0.11957 0.11958' 471.07 '0.25380' 0.25382 0.25381' 0.11957' 0.11956' 0.11956' 471.08  0.19  «0.20434' 0.20436'0.20435' 0.096275' 0,096262' Q096268' 471.09 •0.20438' 0.20438«0.20438' 0.096278' OJ096279 'Q096278' 471.07 1  1  1  The C e l l Constant. 23 G-. Jones and M. Prendergast  have a c c u r a t e l y measured  the s p e c i f i c conductance of 1 demal, 0.1 demal, and 0,01 demal potassium c h l o r i d e s o l u t i o n s . The standards used f o r c a l i b r a t i n g the c e l l were the 0.1 and the 0.01 demal s o l u t i o n s . The s o l u t i o n s were prepared t o w i t h i n 0.1 percent o f the; • weight r e q u i r e d  and a l i n e a r i n t e r p o l a t i o n used t o o b t a i n the  exact s p e c i f i c conductance o f the s a l t . The solvent  conduct-  - 22 -  ance was  added t o t h i s value and the sum taken as being the  s p e c i f i c conductance of the s o l u t i o n which, when m u l t i p l i e d by the r e s i s t a n c e measurement on the c e l l ,  gave the c e l l  con-  s t a n t . Although the r e s u l t s obtained f o r e i t h e r s o l u t i o n are p r e c i s e , ( t a b l e 2) 0.6%  a s e r i o u s i n c o n s i s t e n c y of the order of  i s seen t o e x i s t between the v a l u e s obtained f o r each  solution.  TABLE 2.  C e l l constant V a l u e s U s i n g 0 . 1 •  0.1  Molar  0.01  1  »  1.3109  1  '»  1.3104 1.3103 1.3104 1.3102  i' ' '  '  and  Ifolar  1.3043 1.3041 1*3045 1.3046  0.01  Molar S o l u t i o n s .  »  » » t  » 1 . 3 1 0 4 ± 0.0001 < 1 . 3 0 4 4 i 0 . 0 0 0 2 '  This, i n c o n s i s t e n c y suggested  some i n t r i n s i c  t h e d e s i g n of the c e l l . In o r d e r t o determine the natuis of t h i s v a r i a t i o n , the c e l l at  error i n  more e x a c t l y  constant was  measured  other c o n c e n t r a t i o n s u s i n g the conductance data r e p o r t e d  by T. Shedlovsky,  A.S.  Brown, and D.A.  t i o n of 0.02% was  added i n o r d e r t o b r i n g the v a l u e s to the  standard recommended by Jones and  Maclnnes?^ A' c o r r e c -  Prendergast.  - 23 -  The  c e l l constant v a l u e s obtained were p l o t t e d a g a i n s t  the s p e c i f i c c o n d u c t i v i t y o f t h e s o l u t i o n . The r e s u l t i n g graph showed a minimum v a l u e o f c e l l constant a t a spec-  -3 ific  c o n d u c t i v i t y o f 3.32  x 10  mhos. I t should be p o i n t -  ed out t h a t the v a l u e s Of t h e s p e c i f i c c o n d u c t i v i t y f o r s o l u t i o n s lower than 0.01 normal were s u b j e c t t o a s o l vent c o r r e c t i o n g r e a t e r than one percent which s e r i o u s l y r e s t r i c t e d the accuracy and r e p r o d u c i b i l i t y o f those measurements. The  c e l l constant v a l u e s obtained a t v a r i o u s concen-  t r a t i o n s a r e shown i n t a b l e 3 and presented  graphically  i n f i g u r e 6. TABLE 3.  C e l l " c o n s t a n t " v a l u e s at v a r i o u s c o n c e n t r a t i o n s .  Concentration '  Specific Conductance  Resistance  Cell  Constant  0.1 Molar  0.012831  102.13  1.3104  0.01  0.0014139  922.55  1.3044  0.05 Normal 0.0066704  195.52  1.3042  471.07  1.3024  »»  i0.02  n  0.005  tt  0.002  tt  0.00276480.00071915  1817.7  1.3072  0.00072030  1813.6  1.3063  0.00029322  4470.9  1.3110  0.00029493  4443.2  1.3104  0.00029462  4449.2  1.3108  0.00029340  4460.3  1.3086  FIGURE 6  "CELL CONSTANT" VERSUS SPECIFIC CONDUCTIVITY  AT 25°C.  - 24  . I t has  III.  -  DISCUSSION OF RESULTS.  been shown w i t h reasonable assurance, that  c e l l constant  the  of the conductance c e l l used v a r i e s w i t h the  s p e c i f i c c o n d u c t i v i t y of the s o l u t i o n being measured. Of the s e v e r a l f a c t o r s t h a t may  cause t h i s , the d e s i g n  of  the p o r t i o n of the c e l l over whiosh the v o l t a g e drop i s measured i s emphasised by Gordon as being the most importa n t . The  probe e l e c t r o d e s used by Gordon were p r e v i o u s l y  d e s c r i b e d . T h e i r d e s i g n was narrow w e l l d e f i n e d ference an exact  proposed p r i m a r i l y to  obtain  s l i t s across which the p o t e n t i a l & i f -  can be measured and  f o r r i g i d i t y , thus  ensuring  o r i e n t a t i o n f o r each run. In t h i s r e s e a r c h  probe e l e c t r o d e s were m o d i f i e d have s t i l l  been r e t a i n e d . One  the  but the e s s e n t i a l f e a t u r e s notable  d i f f e r e n c e however  i s t h a t the e l e c t r o d e s u r f a c e of Gordorfs probes e x i s t e d o n l y on one  s i d e ; on our probes the complete circumferahce  o f the wire i s a c t i v e . I t i s p o s s i b l e t h a t t h i s f a c t o r  may  cause, i n p a r t , the observed v a r i a t i o n of c e l l  constant  but  i t should  do  i t is difficult  t o see  any  exact  reason why  so. The width of the profr  e  e l e c t r o d e s was-0.081 c e n t i -  meters. T h i s corresponded t o one-onehundreth of the tance between them, but  i t has  dis-  not been p o s s i b l e to math-  - 25  -  e m a t i c a l l y r e l a t e the IR drop across  t h e i r surface  the experimental change i n c e l l constant. the product of the r e s i s t a n c e and  t o see why should  The  and  s i n c e these  another, i t i s d i f f i c u l t  the ohmic drop across the e l e c t r o d e  cause any  change i n c e l l  s i d e extensions  since  s p e c i f i c conductance of  the e l e c t r o l y t e g i v e s the c e l l constant, are i n v e r s e l y p r o p o r t i o n a l , t o one  In f a c t ,  to  surface  constant.  connecting  the e l e c t r o d e s t o  the  main body of the c e l l were designed to prevent d i f f u s i o n o f the e l e c t r o d e m a t e r i a l s  to the c u r r e n t - c a r r y i n g e l e c t -  r o l y t e . I t i s p o s s i b l e t h a t the e r r o r i n our  c e l l comes  from the p o s s i b l e v a r i a t i o n of the path of the c u r r e n t i n these s i d e arms. With a concentrated  e l e c t r o l y t e one  might  r e a s o n a b l y expect the i o n s to f l o w i n s t r a i g h t p a r a l l e l l i n e s past these e x t e n s i o n s .  However, i f the number of  ions a v a i l a b l e to carry current sent  i n the s i d e arms may  i s decreased, those  pre-  take an a c t i v e p a r t i n c a r r y i n g  the c u r r e n t thus i n c r e a s i n g the d i s t a n c e across which the p o t e n t i a l drop i n the c e l l i s measured. T h i s  possibilty  however would o n l y e x p l a i n the part of the curve i n which the apparent c e l l constant The for  i s increasing.  f o r e g o i n g d i s c u s s i o n does not  the observed phenomena and  work should i n causing  adequately account  i t i s evident  be done to r e v e a l what f a c t o r s the c e l l constant v a r i a t i o n .  that f u r t h e r are,operative  -  The  26 -  e f f e c t of c u r r e n t f l o w i n g through the s i d e arms  could be e l i m i n a t e d by j o i n i n g them t o the body o f the c e l l w i t h f i n e s h o r t c a p i l l a r i e s . An attempt ewas made i n t h i s r e s e a r c h t o do so but t h e r e s u l t i n g s t r a i n s i n t h e c e l l caused i t t o be v e r y f r a g i l e and i t had t o be d i s c a r d e d . However s i n c e then, for  another technique  has.been suggested  use i n c o n s t r u c t i n g such a c e l l and i t i s hoped t h a t  another o f t h i s d e s i g n w i l l  soon be made and t e s t e d .  ' I t was suggested t h a t because t h e probe e l e c t r o d e s used' i n t h i s r e s e a r c h were a c t i v e over the whole f e r a n c e o f the wire, fact  circum-  an e r r o r might be i n t r o d u c e d . T h i s  could be i n v e s t i g a t e d by s e a l i n g platinum wire i n t o  a s o f t g l a s s rod and c o v e r i n g a l l but a narrow s l i t  with  s o f t g l a s s . Thus t h e e l e c t r o d e design o f Gordon would be a c c u r a t e l y copied but t h e d i f f i c u l t  platinum d i s c t o g l a s s  s e a l would be e l i m i n a t e d . One  can see t h a t a c o n s i d e r a b l e e r r o r e x i s t s i n t h e  s o l v e n t c o r r e c t i o n a p p l i e d i n these measurements because of the doubt i n v o l v e d i n u s i n g a p a r t i c u l a r value of the c e l l constant. T h i s e r r o r i s probably  o f the order of  1 o r 2°/o , but may be,as h i g h as 5%. However, the measurement o f -Hue Solvent conductance could be f a c i l i t a t e d by c a l i b r a t i n g a simple  c e l l o f A.C. design and measuring  - 27  -  the r e s i s t a n c e w i t h a vacuum'tube v o l t m e t e r . The meter should of course be c a l i b r a t e d over the necessary  range  u s i n g a standard r e s i s t a n c e i n order to o b t a i n the d e s i r e d accuracy. The method cannot be used w i t h the D.C.  c e l l d e s c r i b e d because of the r e s i s t a n c e i n the  connecting arms of the probe e l e c t r o d e s . Although  the c a l i b r a t e d c e l l does not have a constant  c e l l f a c t o r f o r a l l v a l u e s of s p e c i f i c conductance, i t has been shown t h a t f o r a p a r t i c u l a r s o l u t i o n  reproduc-  a b l e r e s u l t s can be o b t a i n e d w i t h i n one or two  parts i n  ten  thousand. I t i s b e l i e v e d t h a t the c e l l could be used  t o measure unknown s o l u t i o n s w i t h s p e c i f i c  conductances  i n the range c a l i b r a t e d . P r e l i m i n a r y t e s t s would of be necessary on known s o l u t i o n s , and  i f accurate r e s u l t s  were o b t a i n e d , measurements could be c a r r i e d out on s o l u t i o n s as was  originally  intended.  course  DgO  - 28 -  IV.  BIBLIOGRAPHY  (1)  S. Sheldon,  Ann. P h y s i k , 34, 122,  (2)  E . Newbery,  J . Chem. S o c ,  (3)  E.D. Eastman,  (4)  C  (5)  J.N. Bronsted and R.F. N i e l s e n ,  113,  (1888) 701, (1918)  4 2 , 1648, (1920)  J.A.C.S.,  M a r i e and W.A. Noyes J r . ,  J.A.C.S., 4^, 1095, (1921) T r a n s . Faraday S o c , 31, 1478, (1935)  (6)  L,V. Andrews and W.E. M a r t i n ,  (7)  H.E, Gunning and A.R. Gordon,  C.C. Benson and A.R. Gordon, (8)  R.F. Palmer and A.B S c o t t ,  (9)  P. Debye and E . Huekel,  (10)  P. Debye and H. Falkenhagen,  (11)  L . Onsager,  ibid,  J.A.C.S., 60, 398, (1938) J . Chem. 10, 126, 11, 18, i b i d , 13,  Phys., (1942) (1943) 4 7 0 , (1945)  J.A.C.S., 72, 4821, (1950)  Physik Z., ibid,  24,  185, 305, (1923)  29, 121, (1928)  27, 388, (1926) 28, 277, (1927)  (12)  T, Shedlovsky, T.  J.A.C.S., 54, 1411, (1932)  Shedlovsky and A.S. Brown, i b i d ,  G, Jones and C.F.. B i c k f o r d , (13) T. Shedlovsky, i b i d , (14)  ibid,  5jS, 1066, (1934) 5p_,  602, (1934)  54, 1405, (1932)  J . L . Morgan, O.M. Lammert, and M.A. Campbell, J.A.C.S., £3, 454, (1931)  (15)  A.S. Brown and D.A. Maclnnes, i b i d ,  57, 1356, (1935)  (16)  A.S. Brown ,  ibid,  (17)  H.Wo Patton,  J . Chem. Ed., 2 7 , 553,' (1950)  (18)  D.J. LeRoy and A.R. Gordon,  56, 6 4 6 , (1934)  J . Chem. Phys., 6, 398, (1938)  - 29 -  (19) H. Basset and A.S. Corbet, J . Chem..Soc., 125, (20) W. Carmondy,  1660, (1924)  J.A.C.S., j>l, 2901, (1929)  (21) Handbook of Chemistry and P h y s i c s ,  thirty-first  e d i t i o n , Chemical Rubber P u b l i s h i n g Company. (22) C P . Baxter and C C . Wallace, (23)  J.A.C.S., 3 0 , 70, (1916)  G. Jones and M. Prendergast, J.A.C.S., 59, 731, (1937)  (24) T. Shedlovsky, A.S. Brown, and D.A. Maclhnes, Trans, Eleetrochem. S o c , 66, 165, (1934)  -  30  -  PART I I . MEASUREMENT OF STRAIN POTENTIALS  - 31  -  MEASUREMENT OF STRAIN POTENTIALS I . INTRODUCTION HISTORY Most metals or a l l o y s of i n d u s t r i a l importance are a t tacked  by the common environments and  deposit s o l i d  corr-  o s i o n products t h a t are compounds of t h a t m e t a l . I t has been shown t h a t when m e t a l l i c couples  are i n t r o d u c e d  to  c o r r o d i n g environments, one  of the metals w i l l  the other assuming c a t h o d i c  p r o p e r t i e s . T h i s phenomenon  i s a l s o observed between two when one  corrode,  p o r t i o n s of a s i n g l e metal  of these p o r t i o n s i s subjected  t o mechanical  s t r a i n . The work undertaken has a c c u r a t e l y i n d i c a t e d the magnitude of t h i s behaviour f o r #18 copper w i r e s s u b j e c t e d The s i o n has  A.W.G. s o f t drawn  to various s t r a i n i n g loads.  development of the e l e c t r o l y t i c theory of c o r r o stimulated  r e s e a r c h i n the f i e l d  of s t r a i n  pot-  e n t i a l s . T h i s s u b j e c t , d e a l i n g w i t h the r e s u l t i n g change i n the e l e c t r o d e p o t e n t i a l of a metal under mechanical s t r a i n , was  f i r s t i n v e s t i g a t e d i n 1894  by T. Andrews  s i n c e t h a t time very l i t t l e r e s e a r c h has The  r e s u l t s of e a r l y workers '3>4,  ficult  2  a r e  conclusions  but  been c a r r i e d f o r t h .  haphazard and  to reproduce. Even the more recent  1  dif-  experimental  d i f f e r i n many r e s p e c t s . An e f f o r t has  been  made i n t h i s r e s e a r c h , t h e r e f o r e , t o develop c o n s i s t e n t t e c h i n q u e s t h a t can he e a s i l y c o p i e d . The  i n v e s t i g a t i o n r e p o r t e d i s concerned,  most p a r t , w i t h the r e s u l t s obtained on #18  f o r the  A.W.G. s o f t  drawn copper w i r e . P r e v i o u s researches o f t h i s type on  5 copper wire were preformed  by L.V. N i k i t m , L.R. Gautam  and J".B. J h a ^ O.K. M i n i a t o ? B. McDonnell^ The  and R.D. Jamieson?  r e s u l t s o f N i k i t i n are i n reasonable agreement w i t h  o u r s . The paper o f Gautam and J h a / however, r e p o r t s that the s t r a i n e d w i r e became more c a t h o d i c i n copper  sulphate  s o l u t i o n which c o n t r a d i c t s our o b s e r v a t i o n s . The other works mentioned a r e the r e s u l t s o f t h e s i s  investigations  c a r r i e d on a t the U n i v e r s i t y o f B r i t i s h Columbia. The f i r s t of these, performed  by O.K. M i n i a t o , u t i l i z e d  a ballistic  galvanometer, as a d e t e c t i n g instrument. The r e s u l t s r e p o r t ed by M i n i a t o have not been confirmed o r s however, and i t appears  by other i n v e s t i g a t -  t h a t some lamentable  error,  p o s s i b l y i n the c a l i b r a t i o n o f the galvanometer, has o c c u r r e d . The r e s u l t s o f McDonnell have been shown t o be q u i t e v a l i d f o r runs s i m i l a r t o ours, but i n most cases the exact v a l u e s o b t a i n e d were c o n s i d e r a b l y lower  than  those obtained i n t h i s i n v e s t i g a t i o n . I n J a m i e s o n s work f  the main c o n s i d e r a t i o n s were g i v e n t o the change o f pote n t i a l over l o n g p e r i o d s o f time and do not r e a d i l y compare w i t h our  results.  #The a b s t r a c t r e p o r t e d by A.O.  38,  5459, (1944),  more a n o d i c .  A l l e n , Chem. Abs.,  s t a t e s t h a t the stp'ained wire became  - 33 -  THEORY Theoretical considerations  of s t r a i n p o t e n t i a l s have  been as haphazard as the experimental work. E f f o r t s have been made t o c o r r e l a t e t h e magnitude o f the developed p o t e n t i a l t o such concepts as s o l u t i o n pressure,  modulus  o f e l a s t i c i t y , and f r e e energy, but l i t t l e progress has been a c h i e v e d . The g r e a t e s t  e r r o r apparent i n these e f f o r t s  i s the, assumption t h a t a l l t h e energy i s s t o r e d as potenti a l energy. R.W. G o r e n s e n  1 0  has q u i t e c l e a r l y c o n t r a d i c t -  ed t h i s assumption by s t a t i n g t h a t t h e energy o f deformation i s s t o r e d as p o t e n t i a l energy and heat energy. The l a t t e r would, i n t h i s case, be r a p i d l y t r a n s m i t t e d  through the  body/ o f t h e e l e c t r o l y t e and thus be u n a v a i l a b l e ! 7  Other t h e o r e t i c a l approaches a r e p o s s i b l e however, Goranson has o u t l i n e d i n d e t a i l t h e o r e t i c a l c o n s i d e r a t i o n s of s t r e s s e d s o l i d s . I t i s p o s s i b l e that t h e concepts presented by Goranson c o u l d be a p p l i e d t o t h e p a r t i c u l a r case under c o n s i d e r a t i o n and, i n c o n j u n c t i o n w i t h t h e modern t h e o r i e s o f e l e c t r o d e p o t e n t i a l s , q u a n t i t a t i v e l y e x p l a i n t h e phenomenon observed. One might a l s o  consider  the f a c t t h a t c o r r o s i o n o f metals has been observed t o t a k e p l a c e p r e f e r a b l y on a p a r t i c u l a r c r y s t a l  # A d i s c u s s i o n by. P r o f . J.W. R i c h a r ds  plane  1 1  and Mr. W.H. Walker  (Trans. Elchem. Soc, 11, 168, (1907) ) concluded t h a t heating  e f f e c t could not cause t h e observed change i n pot-  e n t i a l . However, t h e r e s u l t s obtained and  this  by N i k i t i n on copper  s i l v e r wires suggests t h a t the momentary change i n temp-  e r a t u r e should  be i n v e s t i g a t e d .  - 34 -  thus s u g g e s t i n g a d i f f e r e n t p o t e n t i a l belonging t o each p l a n e . Perhaps i n s t r e t c h i n g the metal, t h e l e s s  inert  plane o r planes are exposed and g i v e r i s e t o t h e observed change. The r e s t o r a t i o n o f the e l e c t r o d e t o approximately i t s o r i g i n a l value would correspond then t o t h e r e o r i e n t ation of the c r y s t a l s to positions of greater s t a b i l i t y . Another t h e o r e t i c a l approach c o n s i d e r s the p o t e n t i a l t o be due t o r u p t u r e s produced  i n a s u r f a c e f i l m on t h e metal  thus exposing a new s u r f a c e t o the e l e c t r o l y t e . The r e s u l t s presented i n t h i s t h e s i s i n d i c a t e q u a l i t a t i v e l y t h a t t h i s may be t h e c o r r e c t t h e o r y , but the other f a c t o r s are v e r y l i k e l y contributing  also.  Although an exact t h e o r y has not been presented it  here,  i s hoped t h a t the suggestions made may lead t o a quant-  i t a t i v e e x p l a n a t i o n o f s t r a i n p o t e n t i a l s i n the f u t u r e . Such a t h e o r y would undoubtably ledge o f t h e nature of metals  c o n t r i b u t e t o our know-  and t h e i r c o r r o s i o n , and  p o s s i b l y c o n t r i b u t e t o our knowledge o f e l e c t r o d e potentials.  -  II.  35  -  EXPERMINTAL TECHNIQUES AND  DESCRIPTION OF APPARATUS AND  RESULTS  EXPERIMENTAL PROCEDURE  P r e p a r a t i o n ..of S o l u t i o n s . The s o l u t i o n s were prepared by weighing the r e q u i r e d amount of copper sulphate to t h e n e a r e s t m i l l i g r a m and adding i t t o d i s t i l l e d water i n a v o l u m e t r i c f l a s k . No weights or the  c o r r e c t i o n s were a p p l i e d t o the  flask.  The C e l l and S t r a i n i n g Apparatus. The a l l g l a s s shown i n p l a t e 2 , was  c o n s t r u c t e d from a 500  cell,  milliliter  round bottom f l o r e n c e f l a s k . The d e s i g n i s c o n s i d e r e d an improvement over p r e v i o u s types of c e l l s used s i n c e contamination from rubber parts' i s e l i m i n a t e d . The c e l l  ill-  u s t r a t e d was made so t h a t an atmosphere of n i t r o g e n could be c o n v e n i e n t l y kept over the s o l u t i o n i f d e s i r e d . D u r i n g a run, the two  copper w i r e s i n v e s t i g a t e d were  supported on a wooden frame by heavy i n s u l a t e d hooks and passed i n t o the s o l u t i o n through the c a p i l l a r i e s on the c e l l . S c a l e pans were a t t a c h e d to the f r e e ends and the weights added by hand. C o n s i d e r a b l e care had to be taken i n adding the weights  s i n c e any s l i g h t dropping would  a p p r e c i a b l y i n v a l i d a t e the measurements. The Potentiometer and E l e c t r o n i c V o l t m e t e r . The e n t i a l d i f f e r e n c e between the s t r a i n e d and u n s t r a i n e d w i r e s was measured by two methods. The f i r s t method  pot-  to follow page 35  PLATE 2  THE STRAIN POTENTIAL CELL  - 36  u t i l i z e d a Leeds and Northrup p o r t a b l e potentiometer w i t h a range of e i t h e r zero t o f i f t e e n or zero t o s e v e n t y - f i v e m i l l i v o l t s and a b u i l t i n galvanometer. was  A p r e l i m i n a r y run  n e c e s s a r y t o i n d i c a t e the approximate  peak p o t e n t i a l .  Having obtained t h i s v a l u e the potentiometer was weights  added t o new w i r e s . The potentiometer was  at a l l times d u r i n g a run thus e l i m i n a t i n g any  set and t h e balanced  possibility  of imposing an excess v o l t a g e on the wires from the potentiometer c i r c u i t . In the second method the p o t e n t i a l d i f f e r e n c e was measured w i t h an e l e c t r o n i c m i l l r v o l t m e t e r c o n s t r u c t e d i n t h i s l a b o r a t o r y . The ed i n f i g u r e 7,  instrument,  Illustrat-  i s a m o d i f i c a t i o n of the v o l t m e t e r suggest12  ed by H.S.  Burr, C.T.  Lane, and L.F. Nims  f o r the measure-  ment of s m a l l p o t e n t i a l s . I n o p e r a t i o n , the instrument  was  found t o be extremely u n s t a b l e and any s m a l l e l e c t r i c a l d i s t u r b a n c e s would d e s t r o y i t s balance. However, some runs were conducted  s u c c e s s f u l l y w i t h i t which agreed w i t h the  p o t e n t i o m e t r i c measurements.  to follow page 36  l - - 1^- v o l t s  A  3  c  1 - - 90 l -  Vl  "  °3 - - lk  ••  R  £  ?z —  2  R  3  R  4  -  10,000 ohms 6,810  "  6 " - (wire wound)  2  —  1G4GT 20 ohms (w.w.)  3,000  "  -  25  "  V4 -- 25,000  "  (linear  1,000  "  (w.w. )  " "  V  l - - 1C megohms  R  FIGURE 7  - 3  0.1 megohms  5  Tl, T  - • lb  c  S  V  3  5 —  V  6  500  V  7  20  ELECTRONIC MILLIVOLTMETER CIRCUIT  - 37 -  EXPERIMENTAL RESULTS E l e c t r o d e P o t e n t i a l v e r s u s Time.  Three preliminary-  runs were made t o study t h e decay of the developed  pot-  e n t i a l u s i n g 0 . 0 5 N CuSO^ s o l u t i o n . Weights were added and the p o t e n t i a l recorded a t s h o r t i n t e r v a l s o f time. Any i n i t i a l emf. was s u b t r a c t e d from t h e recorded v a l u e s and the r e s u l t a n t d i f f e r e n c e c a l l e d t h e change i n the e l e c t r o d e p o t e n t i a l . The r e s u l t s obtained a r e t a b u l a t e d below, and presented g r a p h i c a l l y i n f i g u r e 8 . F o r convenience, the p o i n t s obtained i n p e r i o d s of time corresponding t o a few seconds have not been l i s t e d i n t h e t a b l e . The  a b s c i s s a (time) f o r r u n #5 has been d i s t o r t e d  i n o r d e r t o c o r r e l a t e t h e data obtained w i t h a 7 k i l o g r a m s t r a i n i n g weight w i t h t h e d a t a obtained w i t h t h e same weight i n run #6. These t h r e e runs were measured w i t h the potentiometer, but l a t e r two s i m i l a r runs were made u s i n g t h e potentiometer on one and t h e vacuum tube v o l t m e t e r on t h e o t h e r . The r e s u l t s (not presented here) are c o n s i s t e n t w i t h t h e previous determinations.  - 38 -  TABT.E 4 . E l e c t r o d e P o t e n t i a l versus Time TIME  RUN #5 -^E.P. LOAD  0 min. 5 Kgm. 1 2 3 4 •v 5 6 7 8 13 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 7 Kgm. 37 38 39 40 41 42 43 9 Kgm, 44 45 50 55 56 57 58 59 60 62  1.75 mv, 1.40 1.12 0.99 0.86 0.81 0.74 0.69 0.65 0.52 0.36  0.33  2.85 2.61 2.33 2.08 1.90 1.77 1.66 2.86 2.33  RUN #6 LOAD -AE.P.  RUN #7 LOAD -AE.P.  0,50 mv. 0.39 0.33 0.30 0.30 0.29 0.28 0.27 0.26 0.01 7 Kgm. 0.14 3.27 2.86 2.51 2,32 2.12 1.98 1,87 1.79 8 Kgm. 1.70 3.04 2.72 2.45 2.24 2.10 9 Kgm. 1.99 1.88 3.12 2.61 2.31 2.13 1.98 1.89 1.78 1.70 1.53 1.35 1.14  5 Kgm.  5 Kgm.  1.66 mv. 1.28 1.11 0.99 0.87 0.84 0.77 0.73 0.69 0.56 0.46  0.42 0.44  7 Kgm.  5.6 4.38 3.60 3.26 3.02 2.85 2.53  10  80 " w  in  30  40  so  Mtmnncs  O H FIGURE 8  NEGATIVE  CHANGE I N E L E C T R O D E P O T E N T I A L  VERSUS TIME I N 0 . 0 5 N  CuS0  4  SOLUTIONS  | » CD 03 03  - 39 -  Peak P o t e n t i a l versus S t r a i n . U s i n g 0.05N CuSo^ s o l u t i o n as the c o n n e c t i n g e l e c t r o l y t e , t h e eous e f f e c t o f sudden s t r a i n s was observed increments  instantan-  by adding  of weight at d e f i n i t e time i n t e r v a l s and r e -  c o r d i n g t h e peak p o t e n t i a l . As i s shown i n f i g u r e 9 the exact v a l u e s do not always correspond, t e d t o be due t o d i f f e r e n c e s  i n t h e v a r i o u s samples o f w i r e .  The data are t a b u l a t e d i n t a b l e  TABLE 5. TOTAL LOAD 1 Kgm. 2  3 4 5 6  7  8 9 10  Peak P o t e n t i a l versus RUN #8 -AE.P.  0 . 0 mv. 0.0 0.0 0.35 2.35 4.49  RUN #11 -AE.P.  0.06  5.72  4.89  Strain  0.02 mv. 0.08  0.17  1.80  1.21  5.60  5.  RUN #13 -AE.P.  mv.  0.27  4.12 " 5.09 4.83  but t h i s i s expec-  2.66 3.65 3.65  RUN #15 TOTAL -AE.P. LOAD  . 2 Kgm. 3 3.5 4 4.5 4.7 4.9 5.1 5.3 6.3 7.3 8.3 9.3  E f f e c t o f C o n c e n t r a t i o n and E l e c t r o l y t e . potentials  developed  0.00 mv. 0.11 0.18  0.26 0.35 0.44  0.70  1.11 1.54 2.10 4.07  4.71  4.63  The peak  f o r v a r i o u s s t r a i n i n g l o a d s were com^-  pared u s i n g 0 . 5 N , 0 . 0 5 N ,  and 0.0005N CuSO, s o l u t i o n s . The  r e s u l t s presented i n t a b l e  6 and f i g u r e 1 0 ,  show that as  T^AT'lTHO  FIGURE 9.  man  In  KItW.i»U!3  PEAK POTENTIAL VERSUS STRAINING LOAD (Weights added every 30 seconds)  - 40 -  the c o n c e n t r a t i o n decreases, s t r a i n e d wire  the anodic p r o p e r t y of  the  i s enhanced.  TABLE 6 . E f f e c t of C o n c e n t r a t i o n on E l e c t r o d e P o t e n t i a l  TOTAL TIME LOAD min. Kgm.  3 3 4 4 6 6 7 7  0 2 2.15 4.15  4.30 6.30 6.45  8.45 9.00 9.45  8 8  -AE.P. 0 . 5 N CuSO^ POT. POT. mv. mv.  -AE.P. 0.0 5N C u S 0 VTVM. POT. POT. mv. mv. mv.  0.03 0.06 0.03 0.03 0.17  0.12 0.12  0.14 0.58 0.35  0.75 0.59  0.11 0.02 0.02  0.01 0.32 0.18  0.60 0.33 0.70 0.49  A s i m i l a r study was  4  0.12 0.24  0.365  3.11 .1.57 3.61  2.50  0.86 0.45 1.98  1.03  2.18  1.53  0.27 0.14  0.16 0.15  0.40 0.65  0.32 0.37 1.94 1.76  1.00  0.12 0.12  1.00  2.40 2.35 7.10  6.13 4.41  4.85 9.90 7.80  8.30 7.22  using  but c o n s i d e r a b l e  variation  i t i s believed that t h i s  un-  effect  o p e r a t i v e d u r i n g the runs. With the other s o l u t i o n s  t h e r e s u l t s obtained anodic  2.16 1.83  9.62 7.51 12.51 10.68  the  observed i n the normal b i a s p o t e n t i a l between two  s t r a i n e d e l e c t r o d e s and was  0.91 2.61 1.71 3.31 2.81  0.04 0.03  r e s u l t s obtained  MgCl'g s o l u t i o n were i n c o h e r e n t , was  1.49  0.07 0.05  made u s i n g 0.05JM s o l u t i o n s of CuSO. , 4  CuCl2, MgSO^, and M g C l . The 2  "0.10 0.06 0.10 0.81  -AE.P. 0.0005N CuSO^ VTVM. POT. POT. mv. mv. mv.  ( f i g u r e 11, t a b l e 7) show t h a t the  p o t e n t i a l i n MgSO^ s o l u t i o n i s c o n s i d e r a b l y g r e a t e r  than f o r CuSO^ s o l u t i o n , but when u s i n g CuCl2 s o l u t i o n a c a t h o d i c p o t e n t i a l i s developed i n the s t r a i n e d e l e c t r o d e .  t o f o l l o w page 40  FIGURE  10  NEGATIVE POTENTIAL  OF  CHANGE  I N  ELECTRODE  FOR VARIOUS  CONCENTRATIONS  CuSO^  ( Weights added every 130 seconds)  - 41 -  TABLE 7. Effect of Different E l e c t r o l y t e s on Electrode Potential.  TOTAL 0.05N CuS0 TIME LOAD' VTYM. POT. min. Kgm. mv. mv. 0  2  2.15  4.15 4.30 6.30  6.45 8.45 9.00  9.45  3 3 4 4  0.12 0.12 0.12 0.24  6  0.36  7  3.11 1.57  6 7 8 8  3.61  2.50  0.10  o.o6  0.10 0.81 1.49 0.91 2.61 1.71 3.31 2.81  VTVM. mv.  0.05N C u C l POT. POT mv. mv  0.12  0.20  0.05N MgS04  4  POT. mv.  VTYM. mv.  POT. mv.  POT. mv.  0.07  0.55 0.70  0.17 0.15  0.12  0.05 0.04  0.03  0.86  0.45 1.98 1.03 2.18  0.90  1.55 4.0 3.70 12,25  7.95 15.35  1.55" 1 0 . 7 8  0.65  0.16  2.83  2.37 12.1 6.70 11.33  9.03  0.37 0.30  0.24 0.55  2.8. 1.41 11.05  5.7 3.83  0.49  0.52  5.25 6.30 4,63 5.70 13.05 9.90 5.25  2  0.25 0.36 0.27 4.46 2.74 5.38 3.70 4.71 4.12  0.15 0.17 0.26 0.13 3.55 2.14 5.75 4.17 5.20 4.66  t o f o l l o w page 41  FIGURE 11,  NEGATIVE CHANGE IN ELECTRODE POTENTIAL FOR VARIOUS ELECTROLYTES. (Weights added every 120  seconds)  - 42 -  III.  DISCUSSION OF RESULTS  I t has been shown t h a t when a copper wire immersed i n an e l e c t r o l y t e i s s u b j e c t e d t o mechanical s t r a i n s an e l e c t r o m o t i v e p o t e n t i a l i s produced  dependent on the mag-  n i t u d e o f the s t r a i n i n g l o a d , the c o n c e n t r a t i o n o f the e l e c t r o l y t e , and t h e components o f the e l e c t r o l y t e . The first  runs performed  i n t h i s r e s e a r c h have  demonstrated  t h a t t h e r e l a x a t i o n o f t h i s p o t e n t i a l i s approximately e x p o n e n t i a l thus s u g g e s t i n g some k i n e t i c process i n ope r a t i o n . I t i t i s assumed t h a t i n CuSO. s o l u t i o n a s u r f a c e  it-  l a y e r o f copper oxide e x i s t s on t h e metal which i s rupt u r e d when t h e wire i s s t r e t c h e d , t h i s process c o u l d be the renewal o f the oxide f i l m by t h e equations 2 Cu° -I- 20H~ Cu 0 2  —*-  1- 20H~ —*  Cu 0  + H 0  + 2(e)  2CuO -r- H 0  + 2(e)  2  2  2  T h i s t h e o r y i s a l s o supported by the d a t a p l o t t e d i n f i g ure 9. I t i s seen t h a t below 4 kilograms v e r y l i t t l e pote n t i a l d i f f e r e n c e i s developed and above 7 kilograms t h e p o t e n t i a l developed  (approximately 5 m i l l i v o l t s i n 0.05N  CuSO^ s o l u t i o n ) i s independent  o f the s t r a i n i n g l o a d . I f  one p o s t u l a t e s t h a t t h e s u r f a c e f i l m s t r e t c h e s w i t h the w i r e up t o a c r i t i c a l s t r a i n i n g l o a d a f t e r which f r a c t u r e s appear i n t h e f i l m , the evidence supports the p o s s i b l e  - 43 -  t h e o r y suggested above. However, t h i s evidence p o i n t Vo  could a l s o  the p o s s i b l e d i s o r i e n t a t i o n of the c r y s t a l s i n  the metal,  but s i n c e i t has  been e s t a b l i s h e d t h a t  the  e f f e c t i s dependent on the c o n c e n t r a t i o n of the  electro-  l y t e and the components of the e l e c t r o l y t e , the  surface  f i l m t h e o r y seems more  probable.  The measurements made u s i n g 0.05N CuCl2 s o l u t i o n show a cathodic i n c r e a s e i n the p o t e n t i a l of the s t r a i n e d w i r e . T h i s f a c t can be e x p l a i n e d by assuming t h a t when the s u r f a c e f i l m of oxide i s broken exposing a new  s u r f a c e f i l m of Gv^±2 i s produced by the 2 Cu°+  The  the pure copper,  2 C l " — C u  2  C l  2  +  equation  2(e),  observed change i n the d i r e c t i o n of the e l e c t r o d e  pot-  e n t i a l corresponds then t o a d i f f e r e n t e l e c t r o d e r e a c t i o n and  i t appears t h a t such t h e o r i e s as may  be d e r i v e d from  c o n s i d e r a t i o n of the energy s t o r e d i n the metal,  modulus  o f r i g i d i t y , or c o r r o s i o n on a p a r t i c u l a r c r y s t a l  plane  can be d i s r e g a r d e d . An i n t e r e s t i n g c o n f i r m a t i o n could made on t h i s e l e c t r o d e or s u r f a c e f i l m t h e o r y by  be  substi-  t u t i n g f o r the e l e c t r o l y t e a r e s i s t a n c e l a r g e enough to prevent two  any a p p r e c i a b l e c u r r e n t from f l o w i n g between the  w i r e s . One  would i n t u i t i v e l y expect a p o t e n t i a l d i f -  f e r e n c e t o be developed, but i t i s d i f f i c u l t  to  estimate  what the magnitude or d i r e c t i o n of t h i s p o t e n t i a l might be.  - 44 -  Work i n t h i s f i e l d has been continued  by Mr. R.S.  Dudley, who has measured t h e p o t e n t i a l developed a t v a r i o u s temperatures and so e s t a b l i s h e d a temperature  coef-  f i c i e n t f o r t h e phenomena. The author would l i k e t o suggest t h a t i n f u t u r e work an emphasis should  be placed on  v a r i a t i o n o f e l e c t r o l y t e w i t h c o n s i d e r a t i o n g i v e n t o the p o s s i b l e e l e c t r o d e processes  t a k i n g p l a c e . Some i n t e r e s t -  i n g p o s s i b i l i t i e s not p r p v i o u s l y considered  are s o l u t i o n s  of copper complexes such as t h e copper-ammonium complex or t h e copper-cyanide complex. Because o f t h e low concent r a t i o n of copper ions present s u l t a n t p o t e n t i a l should  i n such s o l u t i o n s , t h e r e -  be h i g h l y anodic,  i b l e t h a t o t h e r f a c t o r s may give unexpected  but i t i s possresults.  P r o f i t a b l e measurements could a l s o be made u s i n g  differ-  ent m e t a l s . Because o f t h e widespread use o f i r o n and s t e e l , measurement o f s t r a i n p o t e n t i a l s on such could be of great i n d u s t r i a l  importance.  couples  - 45 -  IV.  BIBLIOGRAPHY  (1)  T. Andrews, P r o c . I n s t . C i v i l Eng. ( B r ) , 118, 356, (1894)  (2)  C.Hambuechen, B u i . Univ.Wisc. Eng. S e r i e s 2, 8, 235, (1900)  (3) W. Walker and C. D i l l , T r a n s . Am.'. Elchem. S o c , 11, 153, (1907) (4)  P.D. M e r c i a , Met. Chem. Eng., 15,  (5)  L.V. N i k i t i n , Compte. Rend. Acad. S c i . U.R.S.S., 17,;107, (1937) L.R. Gautam and J.B. Jha, Proc. I n d i a n Acad. S c i . , ISA, 350, (1943)  (6)  321, (1916)  (7)  O.K. M i n i a t o , M.A.Sc. T h e s i s ,  (8)  B. McDonnell, M.A.Sc. T h e s i s , ( B r i t . C o l . ) , September, 1948.  (9) R.D.  ( B r i t . Col-), A p r i l ,  Jamieson, B.A.Sc. T h e s i s , ( B r i t . CoL), A p r i l ,  1947.  1950.  (10)  R.W.  Goranson, J . Chem. Phys., 8, 323, (1940)  (11)  H.H.  U h l i g , The C o r r o s i o n Handbook, P48, J . W i l e y and Sons, (1948)  

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