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The determination of small amounts of zinc in ores Francis, Marion David 1949

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\i*<i  fit  THE DETERMINATION OF SMALL AMOUNTS OF ZINC IN ORES  by  MARION DAVID FRANCIS  A Thesis Submitted I n P a r t i a l • F u l f i l m e n t the  Requirements  f o r t h e Degree^ o f  MASTER OF ARTS in  t h e Department of CHEMISTRY  THE UNIVERSITY OF B R I T I S H April,  i  1949  COLUMBIA  of  ABSTRACT The d e t e r m i n a t i o n o f z i n c b y t h e b a c k titration  o f excess potassium  ferrocyanide Is  i n v e s t i g a t e d and f o u n d v e r y a c c u r a t e and s i m p l e t o perform. Is  The u s e o f t h e e x t e r n a l i n d i c a t o r  shown t o b e i n a c c u r a t e a n d u n r e l i a b l e .  Indicator giving the t i t r a t i o n permanganate•  excellent results  of ferrocyanides with  method A  new  i s developed f o r potassium  DEDICATION The  work i n t h i s  thesis  i s dedicated  to J . ALLEN HARRIS, f o r h i s continuous during  PROFESSOR  e n c o u r a g e m e n t and a s s i s t a n c e  the course  of this  research.  TABLE OF CONTENTS Page INTRODUCTION.  1  THE FERROCYANIDE METHOD.  2  The  External  Indicator  and t h e E f f e c t  o f Ammonium C h l o r i d e . The  2  B a c k T i t r a t i o n Method w i t h  Potassium  Permanganate.  10  COMPARISON OF THE PERMANGANATE METHOD  22  CONCLUSIONS AND  26  TREATMENT OF MATERIAL  REFERENCES  28  APPENDIX  1 I d e n t i f i c a t i o n o f t h e Manganese  Ferrocyanide P r e c i p i t a t e .  i  Tables 1(a) & 1(b)  iv  Table 1(c) Table  v  II  v i l  BIBLIOGRAPHY  End o f T h e s i s  TABLES I  Volume V a r i a t i o n  Concentrations II III  Concentrations IV  Variation  Concentration.  c  with  Different  o f NH^Cl.  Volume V a r i a t i o n Variation  of K„Fe(CN)  7  i n Blank Determination  i n Volume o f KMnO^ w i t h  Different  o f Hydrogen I o n . i n Volume o f KMn0  7  12 4  w i t h NH^Cl 12  TABLE OF CONTENTS TABLES  (Continued)  (Continued) V  Variation  i n Volume o f KMnO^ w i t h ( N H ) 3 0  VI  Variation  i n Volume o f KMnO, w i t h Na^SO, 4 2 4  VII VIII  4  Determination  g  13  4  13  o f Z i n c b y Back T i t r a t i o n  18  Comparison o f t h e Methods f o r t h e  Determination  of Zinc  25  FIGURES I  Titration  Presence II  Curve Using K F e ( C N ) 4  i n the ' -  g  o f NB^Cl.  Curve Showing P e r Cent  Error Against  .  Between  '  7 & 8  C o n c e n t r a t i o n o f NH" C1. 4  Ill  & TV  K Fe(CN) 4  g  - KMn0  4  Potentiometrie  Titration V  Variation  the End P o i n t  F a c e 15 o f P o t e n t i a l w i t h Time a t Face  20  THE -DETERMINATION OF SMALL AMOUNTS OF ZINC IN ORES  INTRODUCTION Tho accurate quantitative determination of zinc has been a d i f f i c u l t problem f o r a long time.  One of the  most s a t i s f a c t o r y and yet inconsistent methods i n use, since the beginning of the twentieth century, has been the ferrocyanide method. In 1904 W. G. Waring^ published a comprehensive -  a r t i c l e on the ferrocyanide method, i n d i c a t i n g the many ways i n which errors could be made i n the determination of zinc i n ores.  According to Waring the p r e c i p i t a t i o n  of zinc by ferrocyanide proceedes i n two stages. 4ZnCl +- 2K Fe(CN) 2  4  6  > 2ZBgFe(CN) +• 8KC1 fi  6Zn Fe(CN) + 2 K F e ( C N ) — — > 4KgZa [FeCCNjJg g  6  4  6  5  (1) ( 2 )  2 In 1907 W. H. Seaman  showed the great v a r i e t y of r e s u l t s  that could be obtained by varying the a c i d i t y , the temperature of the t i t r a t i o n , and the concentration of the zinc and proposed optimum values at which to work. In the same year Wm. H. Keen  outlined a method f o r  p u r i f i c a t i o n of a standard zinc solution with which ho tested the accuracy of the ferrocyanide method. Since the time of the above work many other quantitative methods of analysis f o r zinc have been  (2) proposed u s i n g  a great v a r i e t y of reagents  p y r o p h o s p h a t e g r a v i m e t r i c method the mercuric and  zinc thiocyanate  suggested by Stone^,  method, s u g g e s t e d b y S a r u d i  many r e a c t i o n s i n v o l v i n g o r g a n i c  colorimetric  reagents  and g r a v i m e t r i c d e t e r m i n a t i o n s .  t h e s i s , however, I s h a l l b e c h i e f l y Improvement  such as the  of the ferrocyanide  ,  f o r both In  this  concerned with  the  method.  THE FERROCYANIDE METHOD The E x t e r n a l . I n d i c a t o r and t h e E f f e c t . o f Ammonium C h l o r i d e . It  was  e a r l y decided  variables affecting  that  the accurate  t h e number  ferrocyanide  of titration  o f a sample c o n t a i n i n g z i n c were so numerous t h a t systematic variables Acidity.  a  method f o r i n v e s t i g a t i o n must b e u s e d .  The  a r e l i s t e d below with.the. treatment g i v e n  them.  The a c i d u s e d was h y d r o c h l o r i c , t h e optimum  concentration  f o r the determination  0.5 m o l e s p e r l i t e r  according  being  b e t w e e n 0.3 t o  t o the.work o f W a r i n g  6  and  7 Seaman . in  The c o n c e n t r a t i o n u s e d was 0.4 m o l e s p e r  the f i n a l  Temperature. (68  volume o f t h e t i t r a t i o n s o l u t i o n . The t e m p e r a t u r e was h e l d  - 7 2 ) ° C . b y means o f a s t e a m b a t h , 8  conditions being Indicator.  liter  i n this  A saturated  range  constant optimum  between  temperature  .  s o l u t i o n of the standard  I n d i c a t o r , u r a n y l a c e t a t e , was u s e d .  In later  external  work  (3) ferrous Zinc was  ammonium s u l f a t e was u s e d .  Solution. used.  A solution  o f 0.005184 grams p e r l i t e r  S i n c e no h i g h : g r a d e  purity  z i n c was  at t h e time, a combination o f Waring'a method f o r p u r i f y i n g  t h e C. P. g r a d e  s t a n d a r d was c a r r i e d o u t . the  following.  and  five  dried.  zinc  was washed w i t h  alcohol  small precipitate redissblved filtrate  precipitate  of Fe(0H)  3  FegOg and s i l i c a  of z i n c .  was t h e n b u r n e d  and t h i s was d e d u c t e d Later  a solution  o f no N H C 1 was made up f r o m 4  U. S. B u r e a u an a n a l y s i s solutions  o f Standards  formation o f ZnNH P0 4  4  Potassium ferrocyanide.  and t h e n  The r e s u l t i n g  slab  solution.  zinc  time  The  and d e t e r m i n e d  as  from the o r i g i n a l  requiring  the presence  spelters  from the  o f a s p e c i a l h i g h grade,  o f 99.995 p e r c e n t p u r i t y .  were c h e c k e d  treated  t h r e e , t i m e s , and e a c h  was added t© the. m a i n z i n c 3  water  i m p u r i t y was washed c a r e f u l l y ,  and r e p r e c i p i t a t e d  of Fe(0H)  acid,  was t h e n e x p e l l e d , 4  4  accurately  i n dilute hydrochloric  w i t h e x c e s s NH^OH and N H C 1 .  NH C1  and c a r e f u l l y  A p p r o x i m a t e l y t e n grams was t h e n  made b a s i c  10  f o r use as a  three times with d i s t i l l e d  w i t h excess bromine which  weight  zinc  times with r e d i s t i l l e d  weighed, d i s s o l v e d  the  and Keen's  E s s e n t i a l l y t h e p r o c e s s was  The m e t a l l i c  and NH, ( 6 N ) , r i n s e d o  9  available  with  B o t h o f t h e above  f o rcontent o f z i n c by f i r s t , the and s e c o n d ,  t h e f o r m a t i o n o f ZngPgO^.  A s o l u t i o n 0.2096N  (combining  n o r m a l i t y ) was made up f r o m c r y s t a l s f r o m t h e U. S.  Bureau  (4) of  Standards  Time.  with  The t i m e  constant  f o r c o m p l e t e r e a c t i o n was h e l d  of a stable p r e c i p i t a t e being The  constant  time  absorption  minutes.^  4  seconds..  colloidal  was  F a s t e r a d d i t i o n formed  s o l u t i o n with  consequent  high  o f K^Fe(CN)g•  Stirring. efficient  three  of addition of K Fe(CN)g solution  at sixty  an u n b r e a k a b l e  Mechanical  stirring  was u s e d a s b e i n g  t h e most  and s a t i s f a c t o r y .  Dilution. that  allowed  o f 99.97 p e r c e n t .  a t f i v e m i n u t e s , t h e minimum r e q u i r e d t i m e f o r  formation  held  a purity  The volume o f t h e s o l u t i o n  the f i n a l  was a d j u s t e d so  volume w o u l d a l w a y s b e 2 0 0 — 2 m i l l i l i t e r s .  Electrolyte.  The e l e c t r o l y t e u s e d was  recrystalllzed  ammonium c h l o r i d e I n v a r y i n g c o n c e n t r a t i o n s , f r o m 0 » 0 0 t o 1.500  moles p e r l i t e r .  Other f a c t o r s .  The p o s s i b i l i t y  t h a t would a f f e c t cyanide  a r e to be s e r i o u s l y  The of  the accuracy  first  t h e above l i s t e d  concentration variations  of titration  investigation  with  ferro-  consisted i n holding a l l  conditions constant  except the  and o b s e r v i n g t h e  accuracy.  volume o f K F e ( C N )  s t e a d i l y decrease  a s y e t unknown  considered.  o f ammonium c h l o r i d e ,  from The  of factors  4  g  added was f o u n d t o  a s t h e c o n c e n t r a t i o n o f NH^Cl i n c r e a s e d ,  f i n a l l y r e a c h i n g a minimum optimum v a l u e .  Greater  (5) c o n c e n t r a t i o n s o f NH^Cl t h e n g r a d u a l l y i n c r e a s e d the of  ferrocyanide required  insufficient  electrolyte  the c o l l o i d a l  ZngFe(CN)  amounts o f a b s o r b e d with it  t o g i v e an end  the c o l l o i d .  i n solution  potassium With  also,  edges b e f o r e I t has the s o l u t i o n . method o f  4  crystallizing  s o l u t i o n and  so  a c h a n c e t o be an  out  possibly at  the  stirred  completely  t o "the  mechanical  objection  that  the time r e q u i r e d  i t  f o r development  was  of  the  brown u r a n y l f e r r o c y a n i d e p r e c i p i t a t e , (u"0g)gFe(CN) ,  in  6  the spot p l a t e , v a r i e d titration fifteen was  ©f  and  times  tremendously  f o r the blank; slower  considered that  the  that  The  detection d i f f i c u l t .  without  the presence  two  ways:  first,  finely,  i s , the potassium  c y a n i d e p r e c i p i t a t e would a f f e c t  alone.  mo3t o b v i o u s r e a s o n f o r  v e r y s l o w l y and That  blank  s o l u t i o n reagents  f e r r o c y a n i d e p r e c i p i t a t e , . t h e brown u r a n y l  cyanide p r e c i p i t a t e d  in  actual  i n developing, t h e . c o l o r .  s l o w e r r e a c t i o n was,  zinc  f o r the  the b l a n k , b e i n g ten to  course the free, b l a n k , the I  the  into  stirring. D u r i n g the. c o u r s e o f t h e t i t r a t i o n s  observed  occluded  s m a l l amounts o f K „ F e ( C N ) _  T h i s . 13  large  t o o l a r g e c o n c e n t r a t i o n s o f NH C1  the edges o f t h e h o t  crystallizing  consequently  f e r r o c y a n i d e are  i s i m p o s s i b l e t o p r e v e n t i t from  around  With  the f o r m a t i o n of  I s f a v o r e d and  g  point.  volume  t h e end  the excess K.Fe(CN)  of the  ferro-  making zinc  early  ferro-  point determination A  adsorbed  on  the  (6)  surface o f the c o l l o i d a l  zinc, p r e c i p i t a t e ,  and t h u s  p r e s e n t e d more s u r f a c e f o r t h e u r a n y l a c e t a t e  t o act;, a n d  s e c o n d , t h e brown u r a n y l f e r r © c y a n i d e . f o r m e d , a d s o r b e d on the  surface of the zinc  color  developed  difference "end error  development time v a r i e d  The the blank  b y a s much a s 0.05 t o 0.20 m i l l i l i t e r s ,  o f one p e r c e n t ,  indicator  a n d . t h u s t h e brown  and s e t t l e d , much, more r a p i d l y .  i n the c o l o r  point"  precipitate  i s determined  after  addition  basis  of this reasoning  since  t h e end p o i n t  i n the  on a s e t t i m e b a s i s  o f the drop of t e s t  external  (one m i n u t e  solution).  then, I thought  an  On t h e  i tadvisable to  r e - r u n a l l the determinations., each time f i l t e r i n g t h e zinc  precipitate,  washing i t t h o r o u g h l y w i t h h o t water  c o n t a i n i n g HH^CI, and t h e n t r a n s f e r r i n g solution. least  The two t a b l e s  o f r e s u l t s below r e p r e s e n t a t  two and i n some c a s e s  inconsistent) tabulated  i tto the blank  (where r e s u l t s  a s many a s s i x t i t r a t i o n s .  are the averages.  seem t o b e The r e s u l t s  (V) TABLE I Volume V a r i a t i o n with D i f f e r e n t Concentration of (m/1)  N H 4 C I  Concentrations of N H C 1 4  C o r r e c t e d Volume of Titration ( m / 1 )  0.000  0.0467 0.0934 0.140 0.187 0.234 0 . 2 8 0  0.327 0.374 0.420 0.560 0.934 1.401 (Theoretical  of K^etCNjg  Per Cent E r r o r i n Titrations  20.71 20.42 20.35 20.30 20.24  3.03 1.60 1.25 1.00 0.70  2 0 * 2 0  0 * 5 0  20.31 20.34 20.34 20.33 20.35 20.38 20.42  1.05 1.20 1.20  1.15 1.25 1.40 : 1.60  Volume o f K F e ( C N ) g R e q u i r e d 4  a 20.10 m l . )  TABLE I I Volume V a r i a t i o n  TtyVf  V o l . Of Blank (No p p t )  0.000 0.0467 0.0934 0.140 0.187 0.234 0.280 0.327 0.374 0.420 0.560 0.934 1.401  0.70 0.57 0.58 0.55 0.50 0.53 0.51 0.59 0.56 0.57 0.43 0.40 0.42  Cone, © f NH,C1  i n Blank Determination  Per Cent E r r o r Vol. of In B l a n k Blank (In p r e s . of ppt) 0.75 0.70 0.69 0.62 0.59 0.61 0.61 0.68 0.66 0.67 0.49 0.50 0.64  Per  Cent E r r o r In Det»n  Due t o B l a n k  7.0 19.0 16.0 11.0 15.0 13.0 16.0 13.0 15.0 15.5 12.0 20.0 34.0  0.25 0.70 0.60 0.40 0.50 0.40 0.50 0.50 0.50 0.50 0.30 0.50 1.05  F i g u r e I , C u r v e (1.) and C u r v e (2) show n i c e l y the  e f f e c t o f t h e NE C1 on t h e b l a n k d e t e r m i n a t i o n . A  The  frm  IT) ^ 3 * b N r e a e n t In the Blank. ooytuiide jipt. n the Blank. a c t u a l t i t r a t i o n of  C o n c e n t r a t i o n ©f NH.Cl  (M/L)  (8) (1.)  minimum p o i n t s ©f C u r v e correspond Curve  nicely,  (3),  o f Curve  the (2)  This data  a l s o , with  (1)  of  ferrocyanide  absorption  formed.  Internal absorption  w o u l d be  zinc,  4  to run  true  precipitate. also,  of  removed  by  actual reading  light  of  presence  of these  on  a  and  following of  similar  the  from the  of  readings  f o r an unknown q u a n t i t y run  i t  theoretical  actual as  blank. the  e a r l y course  that another source  mination  was  spot  u s i n g the  amount  and. t h i s v o l u m e s u b t r a c t e d  observed  the  distance  constant  a true b l a n k i n the  subtracted  volume r e q u i r e d  The  even i n the  o f z i n c o f known v a l u e ,  During  in  zinc  c o u l d n o t be  a d u p l i c a t e , w o u l d h a v e t o be  calculated  blanks  i n t h e p r e c i p i t a t e a3  g  In the  W i t h each t i t r a t i o n  volume o f f e r r o c y a n i d e  zinc.  possibility,  value,  Therefore  necessary  concentration  the  the  t h e r e f o r e would lower t h e  precipitate.  manner.  on  of K Fe(CN)  the b l a n k below i t s proper  it  o f the  shows a l s o t h e  internal  the  f o r the  t h e minimum p o i n t f o r  would then i n d i c a t e the  washing- and  (2)  Curve  actual titration  from Curve  of absorption  and  In the plate.  same eye  of t i t r a t i o n s  i t  of e r r o r i n the b l a n k  was deter-  size  o f the drop o f u r a n y l a c e t a t e  This  e r r o r was  easily  dropper h e l d a t the  eliminated  same a n g l e  used  by  each  time • Determinations  using  f e r r o u s ammonium s u l f a t e  e x t e r n a l i n d i c a t o r gave a s e t o f r e s u l t s  analogous  to  (9) those  f o r u r a n y l a c e t a t e , t h e maximum-error i n t h e  presence o f the p r e c i p i t a t e being  0.5 p e r c e n t  a t optimum  c o n c e n t r a t i o n o f ammonium c h l o r i d e . In the l i g h t conclusively by  evident  of data  that high  s e t down a b o v e , i t i s accuracy  the use o f the e x t e r n a l i n d i c a t o r .  to o b t a i n r e s u l t s  of greater certain  c a n n o t be It is  accuracy  1.0 p e r c e n t .  Unless  zinc  amount o f u r a n y l . a c e t a t e u s e d  solution,  optimum a c i d i t y ,  time o f development o f i n d i c a t o r electrolyte,  presence  and  other  to,  e r r o r s as h i g h  since is  the concentration  Table  of the p r e c i p i t a t e  are a d d i t i v e .  value  for indicator,  strictly  significance  Table  I and  of the concentration of  ammonium, c h l o r i d e i n o b t a i n i n g , c o r r e c t r e s u l t s . shows t h e v e r y per  cent  steep  e r r o r with  d r o p and t h e s t e e p  rise  so f a r . a s g a i n i n g g r e a t e r  C o m p a r i s o n w i l l be.made l a t e r  with  then  Figure I I  again  increasing concentration.  o f t h e work on e x t e r n a l i n d i c a t o r s was concluded,in  adhered  encountered  .special  of the electrolyte.  I I show t h e c r i t i c a l  0.5 t o  i n the blank,  w i l l be Of  than  concentration of  f a c t o r s already mentioned.are  the e f f e c t s  Impossible  concentration of  color,  a s 5.0 p e r c e n t  obtained  i n the  This  phase  considered  accuracy.  o t h e r methods  developed.  (10)  THE  The  Back T i t r a t i o n  BACK TITRATION METHOD  of Excess  Ferrocyanide with  Potassium  Permanganate * In  1941 a n a r t i c l e  appeared  b y Z. S.  32 M u k h i n a and M. L . M i r o n e n k o . determined and  zinc  c o u l d be  by p r e c i p i t a t i o n with potassium f e r r o c y a n i d e  potassium  potassium  stating that  f e r r l c y a n i d e and t h e n b a c k t i t r a t e d  permanganate u s i n g I n d i g o carmine  with  as an i n d i c a -  tor.  S i n c e t h e o r i g i n a l r e f e r e n c e was n o t a v a i l a b l e ,  first  had t o r u n checks  on t h e b a c k t i t r a t i o n  accuracy  b y r u n n i n g b l a n k d e t e r m i n a t i o n s on t h e p o t a s s i u m cyanide of  s o l u t i o n using potassium  the t i t r a t i o n  The  i n the presence  f e r r o c y a n i d e was p i p e t t e d  In  hydrochloric acid  of  ammonium  chloride.  was t h e n t i t r a t e d titration light  were  ferroConditions  simulated.  i n t o a s o l u t i o n 0.5 m o l a r  c o n t a i n i n g a l s o 0.23 m o l e s p e r l i t e r The s o l u t i o n , h o t a t (60 - 65)°C»  with KMn0 « 4  I t was f o u n d  t h a t no I n d i c a t o r was n e c e s s a r y ,  yellow green  dilution  permanganate. of zinc  I  color  f o r this since the  of the ferrlcyanide  at this  (200 m l ) d o e s n o t h i n d e r t h e d e t e c t i o n o f t h e  end p o i n t * In  the f i r s t  titrations  t h e a b o v e method a c o n s i d e r a b l e e r r o r  t h a t were r u n on ( 0.5 - 2.0 p e r  cent  ) was f o u n d  t o o c c u r and was a t t r i b u t e d  tion  of a f i n e g e l a t i n o u s p r e c i p i t a t e which  to the formainterfered  (11) somewhat w i t h The  the determination  precipitate  was d e t e r m i n e d  formed o n l y i n t h e presence  o f t h e t r u e end p o i n t . t o b e B/fc^FefCNjg a n d  o f an ammonium  In view o f the d i s c r e p a n c y above, I c o n s i d e r e d investigation  i t necessary  o f t h e f e r r o c y a n i d e - permanganate  The f o l l o w i n g method was u s e d .  liters  o f potassium  the  with  titra-  E x a c t l y 40  milli-  f e r r o c y a n i d e were p i p e t t e d i n t o 400  b e a k e r s and t h e s o l u t i o n s  milliliters  mentioned  t o make a t h o r o u g h  tion.  milliliter  salt.#  sulfuric acid  made up t o 190  and w a t e r , t o c o n t a i n a t  end p o i n t , c o n c e n t r a t i o n s o f a c i d  f r o m 0.00 t o 2.00  moles p e r l i t e r . A s e r i e s  o f t i t r a t i o n s were made v a r y i n g  the  and t h e n v a r y i n g t h e c o n c e n t r a -  concentration of acid  tion and  of f i r s t ,  Blanks  no c a s e ,  found  sulfate;  were r u n on t h e w a t e r a n d s u l f u r i c a c i d a n d  even i n t h e p r e s e n c e  a greater t i t r a t i o n  milliliters. of  s e c o n d , ammonium  t h i r d , sodium s u l f a t e ; w i t h a g i v e n c o n c e n t r a t i o n o f  acid. in  ammonium c h l o r i d e j  these  # Notes  Tables  o f t h e s a l t s , was  value f o r the blank  than  there 0.02  I I I , I V , V, a n d V I , show t h e r e s u l t s  experiments.  The c o m p l e t e i d e n t i f i c a t i o n o f t h i s i s given i n d e t a i l In the appendix.  precipitate  (12)  TABLE I I I Variation i n Volume of KMn<>4 With Different Concentrations of Hydrogen Ion Volume of K4Fe(CN)6  Conc» E (m/1)  39.96 ml  0.00 0.10 0.50 1.00 1.50 2.00  Volume of KMnO-4  Difference  % Error  (End Point Obscured) 16.51 0.01 16.48 0.04 16.50 0.02 16.46 0.06 16.43 0.09  0.06  0.24  0.12 0.24 0.54  (Theoretical Volume of KMnO^ Required = 16.52 ml)  TABLE IV Variation i n Volume of KMn0 With HH4CI 4  Concentration Volume of K Pe(CN) 4  6  39.96  Cone. H (m/1) 0.10 0.10 0.10 0.10 0.30 0.30 0.30  Cone, of  Volume of  Diff.  #Error  NH4CI  KMn0  0.000 0.047 0.140 0.187 0.093 0.140 0.187  16.52 0.00 0.00 16.45 0.07 0.42 16.43 0.09 0.54 16.40 0.12 0.73 16.40 0.12 0.73 16.38 0.14 0.85 (End Point Obscured)—  4  (Theoretical Volume of KMn0 Required s 16.52 ml) 4  (13)  TABLE V Variation Volume o f K Pe(CN) 4  6  19.98  i n Volume o f KMnO  Conc.H  Gone, o f  ' (a/D  (NH )gS0  0.10 0.10 0.10 0.10 0.30 0.30 0.30 0.30  4  A  With  (HH.USO  Volume o f KMn0  4  0.010 0.019 0.028 0.038 0.010 0.019 0.028 0.038  ( T h e o r e t i c a l Volume o f K M n 0  Diff.  4  8.28 8.27 8.20 8.37 8.25 8.28 8.30 8.13 4  % Erro]  Required  0.02 0.01 0.06 0.11 0.01 0.02 0.04 0.13  0.24 0.12 0.73 1.30 0.10 0.24 0.48 1.60  r 8.26 m l )  TABLE V I V a r i a t i o n i n Volume o f KMn0 Volume o f K Fe(CN) 4  39.96  6  Conc.H (m/1) 0.45  Cone, o f Na S0 2  4  With N a S 0 2  Volume o f KMn0  4  ( T h e o r e t i c a l Volume o f KMn0  4  Diff.  %  Error  4  17.25 17.27 17.33 17.34 17.37 17.38  0.017 0.035 0.052 0.070 0.087 0.105  4  Required  0.05 0.03 0.03 0.04 0.07 0.08  0.29 0.17 0.17 0.23 0.40 0.46  Z 17.30)  (14) Table accuracy  with  range o f a c i d about  cyanide  concentration  f o r accurate  the increasing  accurate  ence o f as l i t t l e Increasing error.  Inaccuracy  concentration  ammonium c h l o r i d e  really  acid  titration  In the f e r r o -  I n t h e case o f (Table I V ) ,  was made, e v e n i n t h e p r e s Furthermore,  seems t o i n c r e a s e t h e  c o n c e n t r a t i o n does  concentration  This  itation  o f sodium s u l f a t e  moles p e r l i t e r liter  or greater.  o f ammonium s u l f a t e  0.3  of acid,  f r o m 0.00 t o 0.10 ammonium  i n the p r e c i p -  f e r r o c y a n i d e when u s i n g reagent.  potassium  The s a f e  a p p e a r s t o b e f r o m |00.00 -  I n an a c i d  c o n c e n t r a t i o n 0.30 m o l e *  The u s e o f s u c h s m a l l  should  satis-  precipitation.  Thus we c a n s e e t h a t  permanganate f o r t h e b a c k t i t r a t i o n r a n g e f o r ammonium s u l f a t e  materially  i s more  cannot be u s e d as t h e e l e c t r o l y t e of potassium zinc  however,  of at least  i s desired f o rthe zinc  i s satisfactory.  V  In the presence of  of the t i t r a t i o n .  concentration  chloride  per  Involved  V I shows t h a t a t 0.45 m o l e s p e r l i t e r  or l a r g e r  0.03)  IV and T a b l e  a s 0.05 m o l e s p e r l i t e r .  s i n c e an a c i d  moles p e r l i t e r  any  Table  I n t h e c a s e o f t h e ammonium s u l f a t e ,  factory,  The s a f e  appears t o be from  as t h e e l e c t r o l y t e  concentration  the accuracy  Table  of acid.  o f ammonium i o n .  (Table V) I n c r e a s i n g a c i d aid  titration  - permanganate t i t r a t i o n  Increasing  no  a varying  ( 0 . 5 - 1*5) m o l e s p e r l i t e r .  indicate  using  I I I shows a d e f i n i t e c h a n g e I n  be s a t i s f a c t o r y ,  concentrations since the  I  8  o TTi  (15) theory and experiment suggest that ammonium s u l f a t e i s a much stronger agent f o r coagulation than i s ammonium c h l o r i d e , "being of the order 250 to 1 f o r some inorganic 13  sols  and of the order 16 t o 32 times b e t t e r f o r other  sols* The d i f f e r e n c e i n e f f e c t of an ammonium s a l t and a non-ammonium s a l t on the ferrocyanide - permanganate t i t r a t i o n i s w e l l I l l u s t r a t e d by the two graphs. (Figures I I I and I V ) .  Note that the region (A)  bracketed i n Figure I I I i s a region of sharp increase i n p o t e n t i a l but i n r e g i o n (B) i n s t e a d of the p o t e n t i a l continuing to increase sharply i t l e v e l s o f f and then gives the f i n a l l a r g e jump.  The r e g i o n (A) i s accounted  f o r by the f a c t that manganese ferrocyanide has p r e c i p i t a t e d and thus e f f e c t i v e l y removed some of the f e r r o cyanide, g i v i n g a premature end p o i n t .  At the p o i n t of  sudden l e v e l i n g , however, the concentration of f e r r o cyanide has been lowered (by i t s o x i d a t i o n ) below the concentration required t o keep the p r e c i p i t a t e out of s o l u t i o n and so the p r e c i p i t a t e d i s s o l v e s .  The s o l u t i o n  of the p r e c i p i t a t e then keeps the p o t e n t i a l almost constant u n t i l the p r e c i p i t a t e has completely d i s s o l v e d . At complete s o l u t i o n of the p r e c i p i t a t e the p o t e n t i a l again begins t o r i s e r a p i d l y . Figure IV shows the smooth, normal o x i d a t i o n curve and g r a d u a l . r i s e of the p o t e n t i a l u n t i l the true end p o i n t , that i s , the t i t r a t i o n i s a  (16) n o r m a l one that  and  titration  so s h o u l d h e ,  and  i n the presence S i n c e the use  i s , more a c c u r a t e  o f ammonium  use  o f sodium s u l f a t e ,  to  attempt  In  order  ion*  o f an ammonium s a l t  e l e c t r o l y t e does i n v o l v e a s l i g h t l y l a r g e r I thought  to o b t a i n the b e s t r e s u l t s  the  involving  composition  and  accuracy of the back t i t r a t i o n , finally  solution,  137.5  rate  13.5  milliliters  milliliters  o f w a t e r and  milliliters o f 60 d r o p s  a constant  of standard per minute*  speed  o f 6N 2.00  bath  and  then  with  stirring.  potassium  Now  and  t o t h e end  titrations  second 90  then heated  a Bunsen flame erature  the  constant  was  per  was  standard  sulfuric  grams o f  acid,  sodium  t o 7 0 ° C , and  exactly  ferrocyanide run i n at After  the l a s t  drop  s o l u t i o n was  (15  - 20)°C*  19*98 m i l l i l i t e r s  p e r m a n g a n a t e was  was  of  f o r , e x a c t l y three minutes*  cooled f o r f i v e minutes to  mixture  optimum  t o o b t a i n maximum  milliliters  f e r r o c y a n i d e had b e e n added, the  was  the  t h e f o l l o w i n g method  s u l f a t e were m i x e d t o g e t h e r , h e a t e d 19.98  the  developed. E x a c t l y 19.98  zinc  than  electrolyte.  of a stable,  of zinc,  an  Interesting  c o n d i t i o n s f o r the p r e c i p i t a t i o n precipitate  for  error  i t w o u l d be  u s i n g o n l y sodium s u l f a t e as  than  of  stirred The  In a added  water rapidly  cent of the r e q u i r e d standard run  i n i n the c o l d .  the t i t r a t i o n  determined  at  mixture  The  f o r t h r e e m i n u t e s t o 65°C*  point.  the  The  completed  end  at this  over temp-  p o i n t of a l l these  b y means o f a r e s e a r c h m o d e l  (17) Beckman pH A high  Meter converted  temperature  platinum  a h i g h temperature e n c e , were u s e d . mination  calomel The  use  e l e c t r o d e (#1281-X11),  f o r the  o f t h e Beckman f o r t h e end  The  p e r m a n g a n a t e as  when t i t r a t i n g p o t a s s i u m  deter-  p o i n t became a  following reason.  change u s i n g p o t a s s i u m  normal  i t s own  f e r r o c y a n i d e , was  color  indicator,  from  green  o f the f e r r l c y a n i d e ) t o y e l l o w t o orange.  appearence o f the  first  and  e l e c t r o d e (#8970-T) f o r r e f e r -  o f the hack t i t r a t i o n  necessity,  (color  to p o t e n t i o m e t r i c r e a d i n g s ,  faint  orange c o l o r  The  i s the  end  1 5  p o i n t , not potassium  the p i n k  •  In the presence  o f the  f e r r o c y a n i d e p r e c i p i t a t e , however, the  change was  almost  of i d e n t i f i c a t i o n h i g h as 15 p e r  completely  obscured  of the  p o i n t was  end  c e n t were i n c u r r e d .  p o t e n t i o m e t r i c method, t h e n , was  and  when t h i s  use  two  orthophenanthroline  by  method as  the  i t was  compiled. an  f e r r o u s complex.  o f t h e r e a d i n g s were d e t e r m i n e d  nitrobenzene.  of  d e v i s e d and  f o u r r e a d i n g s o f T a b l e V I I were d e t e r m i n e d indicator,  color  used, e r r o r s  The  t h i s method t h a t T a b l e V I I b e l o w , was  last  zinc  The  by last  internal The  i n the presence  of  TABLE V I I  ^  D e t e r m i n a t i o n o f Z i n c by Back  Titration.  V a r i a t i o n With Na S0.. o  Vol*  of  ZnS0  4  Std.  V o l .of K Fe(CN) 4  Cone, o f 6  Na S0 2  Added  4  Cone. . B a c k  Equiv.  of H  V o l . of  Tlt'n KMn0  19.98  39.96  >  15.00  >  r  10.00  f 3 .00  <  >  22.98  >  0.035 0.070 0.105 0.210  K Pe(CN)  With  -  0.45  4  V o l .of K Fe(CN)g 4  6  Req'd by  4  Cale.  Theoret.  %  Wt. o f  Wt. o f  Error  Zinc  Zinc  Zinc  9.02 8.99 8.95 8.88  20.84 20.77 20.68 20.51  19.12 19.19 19.28 19.45  0.0978 0.0982 0.0986 0.0995  0.0999  0.035 0.070 0.105 0.210  11.06 11.02 11.02 10.98  25.55 25.46 25.46 25.37  14.41 14.50 14.50 14.59  0.0737 0.0742 0.0742 0.0746  0.0750  1.73 1.06 1.06 0.53  0.035 0.070 0.105 0.210  13.03 13.18 13.13 13.07  30.10 30.45 30.33 30.19  9.86 9.51 9.63 9.77  0.0504 0.0487 0.0493 0.0500  0.0500  0.80 2.60 1.40 0.00  0.105 0.210 0.210 0.210  8.70 8.67 8.68 8.68  20.10 20.03 20.05 20.05  2.88 2.95 2.93 2.93  0.01473 0.01540 0.01498 0.01498  0.0150  1.80 2.60 0.13 0.13  1  >  '1  2.10 1.70 1.30 0.40  (19) Considerable applying end  the  point.  potential  Beckman t o t h e The  in five  large potential r i s e  to three  point  the  constant tial  recognition of  i n most o t h e r  t i o n r e a c t i o n s , but  one  at  the  o f f again  the  to  eight  end  very  t i t r a t i o n has a t a b o u t 0.75 first  t o 1.5  the  rapidly.  In  the  On  millivolts, eight the  remains constant  s e c o n d s and  a c t u a l peak o f t h e  t i m e , i t was  reaction  of  the  consideration a t 65°C.  g a n a t e and  i s , that  above t h e  addition of  the  sure that fall  i s taken care this  ferrocyanide  was the  of by  the  due  the  end  even a f t e r t h r e e  for five  p o i n t has  minutes the  to a  c a r r y i n g out  the  r e a c t i o n of A graph  p o t a s s i u m permanganate i s shown i n F i g u r e  V.  the -  to  short was  slow This titraperman-  showing  drop This  r e a l l y been reached, potential is s t i l l  10)  Since  oxidation  t h e v a r i a t i o n o f p o t e n t i a l w i t h t i m e f o r one  shows t h a t  (6.5  ferrocyanide.  rapid.  poten-  each  f o r such a  not  temperature the i s very  end  solution  reading  potential lasts  p e r m a n g a n a t e on  At  the  s t e a d i l y drops back again.  n e c e s s a r y t o be  complete, that  tion  then  this  the  p o t e n t i a l remains  from a p p r o x i m a t e l y at  oxida-  approximately  f a r past  millivolts  r i s e began.  p o t e n t i a l s u r g e s up  good  potential  e x t r a d r o p o f p o t a s s i u m permanganate to the negative  a  seconds a f t e r  point,  been run,  in  true  s t r a i g h t forward  m i n u t e s , d e p e n d i n g on how  where t h e  required  p o t a s s i u m permanganate g i v e s  jump, as  begins to f a l l  t e c h n i q u e was  of curve since  well  v  potentiometric  Reading  (Millivolts)  (20) above the s t a r t i n g p o i n t curve, to  F i g u r e V, was  just  one  drop  obtained by  (0.06 ml.)  d r o p was  t h e n added and  the  just  drop  Readings  touched  touched  the  of  the s u r f a c e and  titration  end p o i n t .  t a k e n a s t h a t t i m e when of the  solution.  potential  were t h e n  g r a d u a l f a l l i n g o f f of the  secondary r e a c t i o n s  4  +  r e a c h e d was  c a t a l y s e d by  due the  to the precipitate  I n t h e s e r e a c t i o n s t h e perman-  1  (-1.52) (-1.33)  >J  of a i r by n i t r o g e n , over the s o l u t i o n  d i d not increase  appreciable  production  -4-10 €  SMn*"* -!- 1 0 H „ 0  titrated  drop  dioxide.  2Mn0 *M- 16H  Displacement  taken  potential  i s g r a d u a l l y reduced w i t h the subsequent  o f manganese  The  solution.  z i n c , began t o s e t i n .  ganate  The  from the time the  t h e p o t e n t i a l p l a t e a u was that  the  from the true  of three minutes  The  fact  carrying  z e r o time  o f time i n seconds  over a p e r i o d  after  of the p o t e n t i a l r i s e .  the p l a t e a u p e r i o d by  to  be  any  time. S i n c e t h e p o t e n t i o m e t r i c method i s somewhat  more d i f f i c u l t t h a n i s t o be d e s i r e d , I t h o u g h t use  o f an i n t e r n a l  sensitivity decided # Note. Smith  i n d i c a t o r would perhaps  of the determination.  on was  The  Company and  i s manufactured  i s s o l d under  increase  indicator  orthophenanthroline ferrous  This indicator  that  by  t h e name o f  the the  finally  complex". t h e G.  As  Frederick  "Ferroln".  (21) was  t o be  expected  not permanent.  the c o l o r  The  c h a n g e , however, f r o m  form t o the o x i d i z e d was  so r a p i d  that  to Inhibit  the  t h e d e t e r m i n a t i o n o f t h e end I t was  the e f f e c t  form  point  necessary then to f i n d of the p r e c i p i t a t e  some-  zinc.  was  change.  f o l l o w i n g method u s i n g o r t h o p h e n a n t h r o l i n e  ferrous  t o s l o w down t h e r a p i d  of  was  Nitrobenzene The  found  was  reduced  and b a c k a g a i n t o t h e r e d u c e d  extremely d i f f i c u l t . thing  change a t t h e end p o i n t  c o m p l e x a s I n d i c a t o r was  developed  indicator  and  found  satisfactory. The  r e q u i r e d volume o f z i n c depending  t h e c o n c e n t r a t i o n o f t h e s o l u t i o n , was milliliters  o f 6N  sodium s u l f a t e . that  the f i n a l  t i o n w o u l d be  sulfuric  acid,  and  pipetted^ into  6 grams o f  Enough d i s t i l l e d . w a t e r Volume o f s o l u t i o n  a p p r o x i m a t e l y 200  upon  was  at the  anhydrous  t h e n added  end  milliliters.  of the The  acid  then heated  to  t h e r e q u i r e d volume o f f e r r o c y a n i d e added  drop by drop was  stirred  over a Bunsen f o r f o u r  to give just for exactly  a slight  excess.  three minutes  and  The  c o o l e d t o (15 - 2 0 ) ° C . f o r f i v e  Three m i l l i l i t e r s  o f p u r e n i t r o b e n z e n e were now then the  second  ferrocyanide  f o r the back t i t r a t i o n  added.  # Note.  precipitate  t h a n 0.10  The  grams o f  and  zinc.  of zinc  minutes  solution  then p l a c e d i n  a w a t e r b a t h and  with vigorous s t i r r i n g  so  titra-  s o l u t i o n was 7 0 ° C . and  15  minutes. added  portion  of  Approximately  s h o u l d n o t c o n t a i n more  (22)  90 p e r c e n t o f t h e r e q u i r e d p o t a s s i u m p e r m a n g a n a t e was now r u n i n a n d t h e s o l u t i o n h e a t e d  t o (60 - 6 5 ) ° C .  t h e h o t s o l u t i o n were a d d e d two d r o p s and  then the t i t r a t i o n  was c o m p l e t e d  p e r m a n g a n a t e t o t h e end p o i n t . end p o i n t lasts  i s from orange  from f i v e  on t h e o r a n g e ground  lighting  The c o l o r c h a n g e a t t h e  to a c l e a r green c o l o r  again.  A white base  use o f F e r r o i n  either  i n the presence  of zinc  zinc.  The u s e o f t h i s  indicator  in  taking  a n d good b a c k  as p r e v i o u s l y  applies  or out o f the presence o f i n the straight  f o r the i d e n t i f i c a t i o n  f e r r o c y a n i d e end p o i n t itself  which  a s an i n d i c a t o r  o f f e r r o c y a n i d e i s almost  satisfactory  by the addition o f  are e s s e n t i a l . The  titration  o f 0.05M F e r r o i n  t o t e n seconds b e f o r e g r a d u a l l y  tint  To  ideal  forward  and i s f a r more  o f t h e permanganate -  than t h e u s e o f t h e permanganate  suggested.  T a b l e I I I and T a b l e V I w h i c h  A l l those determinations were made p r e v i o u s l y c a n  b e made even more a c c u r a t e l y i n t h e p r e s e n c e o f F e r r o i n .  COMPARISON OF THE PERMANGANATE A comparison for  o f t h e f i n a l methods d e v e l o p e d  t h e a n a l y s i s o f z i n c was c o n s i d e r e d n e c e s s a r y f o r a  final was  METHOD  e x a m i n a t i o n o f t h e permanganate method.  t o be a comparison  different the z i n c  o r e samples. and t h e n t h i s  Since  this  t h e a n a l y s i s was done on f o u r These  o r e s were t r e a t e d  extracted  zinc  to extract  was a n a l y s e d b y t h e  (23) e x t e r n a l i n d i c a t o r method, and b y  the back t i t r a t i o n  u s i n g b o t h the i n t e r n a l  and p o t e n t i o m e t r i c  determination. tabulated the  indicator  The methods and  i n Table V I I I .  following  their various results  f o u r o r e s were t r e a t e d  o r e samples  were d r i e d  a t 100°C.  A p p r o x i m a t e l y f o u r gram s a m p l e s  w e i g h e d a c c u r a t e l y , p l a c e d i n an liters  acid  effervescence ceased.  The  and  added  and  trated n i t r i c  t h e whole m i x t u r e  near dryness.  milliters  added and The  s o l u t i o n was  trioxide.  heated  o v e r an  then  boiled  added.  s o l u t i o n was  e x a c t l y 100 m i l l i l i t e r s mixture  and  This  open f l a m e t o fumes o f  sulfur  heated  o f water  almost was  method  above  to dryness^,  added t o t h e c o o l e d  t h e n 20 m i l l i l i t e r s , more o f c o n c e n t r a t e d  acid.  Pellets  boiled  f o r 10 m i n u t e s  paper  40  S i n c e i n t h e permanganate b a c k t i t r a t i o n  acid  o f p u r e a l u m i n u m were added and and  containing pellets  filtered  then  concen-  t h e n c o o l e d and acid  milli-  of  i s i m p e r a t i v e t h a t no n i t r a t e be p r e s e n t , t h e  sulfuric  40  and  with  20 m i l l i l i t e r s  of concentrated s u l f u r i c  m i x t u r e was  it  acid  for  s o l u t i o n was  e v a p o r a t e d t o 20 m i l l i l i t e r s  to  by  were t a k e n  erlenmeyer,  of concentrated hydrochloric  warming u n t i l  are  e x t e n s i v e method. The  one h o u r .  The  method  into  the  a beaker  sulfuric  mixture  through  o f aluminum.  # Note, I t has been the e x p e r i e n c e o f t h i s worker t h a t HNOg i s n o t c o m p l e t e l y d r i v e n o f f w i t h t h e f i r s t few m i n u t e s of s u l f u r t r i o x i d e fuming. I t was f o u n d n e c e s s a r y t o evaporate the s u l f u r i c a c i d mixtures almost to dryness b e f o r e o b t a i n i n g complete e x p u l s i o n o f n i t r i c a c i d .  (24) The 125  milliliters  precipitate  filtered  s o l u t i o n was e v a p o r a t e d t o  and 6N ammonium h y d r o x i d e  o f zinc hydroxide  Then 100 m i l l i l i t e r s  just  o f IM c i t r i c  failed acid  excess  was  of c i t r i c  acid,  6M ammonium  100 m i l l i l i t e r s  now added and a l s o 100 m i l l i l i t e r s  s o l u t i o n o f ammonium s u l f a t e .  the  hydrogen and  sulfide.  the exit  tube  to 6 0 ° C , The m i x t u r e  closed.  o f IM s o l u t i o n ,  S i n c e no c o b a l t was p r e s e n t  The volume was t h e n  s o l u t i o n heated  hydroxide.  o f a 20 p e r c e n t  t h e u s e o f ammonium t h i o c y a n a t e f o r t h i s necessary.  to redissolve. were added and  1 6  made n e u t r a l t o m e t h y l o r a n g e b y a d d i n g An  added u n t i l t h e  o r e was n o t  a d j u s t e d t o 800 m i l l i l i t e r s ,  and a i r r e p l a c e d w i t h was t h e n h e a t e d  I t was a l l o w e d  t o 95°G.  t o c o o l and  become s a t u r a t e d w i t h h y d r o g e n s u l f i d e u n d e r t h e p r e s s u r e of  the generator,  allowed a OilM  to settle,  and was s h a k e d  f r e q u e n t l y f o r 40  separated by f i l t r a t i o n ,  solution of c i t r i c  acid  minutes,  a n d washed  saturated with  with  hydrogen  sulfide. When t h e w a s h i n g s were c o m p l e t e p a p e r and r e s i d u e boiled  w i t h 40 m i l l i l i t e r s  hydrogen  s u l f i d e remained  p a p e r was f i l t e r e d with  into  a b e a k e r and  o f 6N s u l f u r i c  u n t i l no more  i n the s o l u t i o n .  The f i l t e r  o u t w h i l e h o t a n d washed r e p e a t e d l y  s m a l l p o r t i o n s o f 200 m i l l i l i t e r s  water. to  ( Z n S ) were d r o p p e d  the f i l t e r  The f i l t r a t e  of boiling hot  containing the zinc  e x a c t l y 250 m i l l i l i t e r s  was t h e n made u p  i n a volumetric  flask.  (25) Aliquots  of t h i s  s o l u t i o n were a n a l y s e d  methods t a b u l a t e d  i n Table  TABLE  f o r zine by the  VIII.  VIII  Comparison o f Methods for Ore Number  Sample Number  the Determination Sample Weight (gms.)  of Zinc.  B a c k T i t ' n Method PotentioInternal metric lAdi.c,. (gms.) (gms.) 0.6349 0.6369 0.5520 0.5525  Ext. Indie Method (gms.) 0.6482 0.5673  1  A B  4.7058 4.1090  4  A B  4.1006 4.2711  0.6369 0.6627  0.6337 0.6632  0.6439 0.6650  6  A B  4.1853 4.0532  0.6925 0.6680  0.6905 0.6695  0.7052 0.6811  8  A B  4.2769 4.1222  0.7789 0.7840  0.7764 0.7471  0.7890 0.7520  .  Thorn Smith Analysis it)  (JO  (jO  (JO  13.49 13.44  13.77 13.81  1  A B  13.54  13.54 13.45  4  A B  15.49  15.53 15.52  15.45 15.53  15.70 15.57  6  A B  16.91  16.55 16.48  16.50 16.38  16.85 17.05  8  A B  18.17  18.21 18.15  18.15 18.12  18.45 18.24  An  examination o f Table  o f t h e two methods o f d e t e r m i n a t i o n , internal  VIII  shows t h a t  potentiometric  or  i n d i c a t o r , t h e most r e l y a b l e a p p e a r s t o b e . t h e  potentiometric.  The t a b l e i l l u s t r a t e s a l s o t h e e x t r e m e l y  (26)  consistent results Ore  #6,  obtained  b y e i t h e r method.  the l a r g e s t s i n g l e d e v i a t i o n from the v a l u e s  r e p o r t e d b y T h o r n S m i t h i s 0.10 mean d e v i a t i o n f o r discrepancy a  slight  slightly  i s accounted  of reducing  f o r by  consequently  method g i v e s  reducing  the p r e s e n c e  s u b s t a n c e i n the  t h e amount  1. gives  extracted  thus i n c r e a s i n g  of reported  results.  The e x t e r n a l I n d i c a t o r method  c e r t a i n value  will  not give  I n the p r e c i p i t a t i o n  but i t s concentration  critical.  Involving  this  while  accuracy  of  t h a n 98.5 p e r c e n t . o f z i n c as  p o t a s s i u m z i n c f e r r o c y a n i d e , an e l e c t r o l y t e necessary  zinc.  TREATMENT OF MATERIAL  consistent results,  2.  is  of  I I the external i n d i c a t o r  consistently high  CONCLUSIONS AND  greater  The  the r e q u i r e d volume i n p o t a s s i u m permanganate  As shown p r e v i o u s l y i n T a b l e  it  and t h e l a r g e s t  any one ore i s 0.06 per cent.  i n Ore #6  amount  per cent,  s o l u t i o n due t o an e r r o r i n t e c h n i q u e ,  and  Ignoring  i s not only  f o r maximum  accuracy  This applies to a l l determinations zinc  precipitate.  3.  The t i t r a t i o n  of ferrocyanide  with  p e r m a n g a n a t e c a n b e made e x t r e m e l y a c c u r a t e l y b y any one of the f o l l o w i n g three methods,.provided that  ammonium  Ion  concentration  i s not present  i n the s o l u t i o n i n greater  (27)  t h a n 0.05M. ( a ) By o b s e r v a t i o n o f t h e end p o i n t b y means o f a  potentiometer. (b) B y u s i n g p o t a s s i u m  as I t s own  indicator. (c)  ferrous Of t h e s e the  t h r e e methods  easiest  the l a s t  to handle,  excellant  and t h e most  with potassium  accuracy  procedure developed  named i s b y f a r t h e f a s t e s t ,  in a  permanganate  I f care i s taken  solution will  with the  a n d c a u t i o n i s u s e d when  end p o i n t b y e i t h e r t h e i n t e r n a l  potentiometer.  satisfactory.  The d e t e r m i n a t i o n o f z i n c  by the back t i t r a t i o n  the  By t h e use o f o r t h o p h e n a n t h r o l i n e  complex.  4.  give  permanganate  determining  indicator  or the  (28)  REFERENCES 1*  W. G. W a r i n g ,  2.  W. H. Seaman, I b i d , 29, I , 205 - 211,  3.  J . Am.  ^W. H. Keen, I b i d ,  Chem. S o c , 26, 4 - 29,  30, 904,  (1904).  (1907).  (1908).  j  4.  Stone,  5.  I . Sarudl,  6.  W. G. W a r i n g ,  7.  W. H. Seaman, l o c . c i t .  8.  W. H. Seaman, l o c .  9.  W.  10.  W. H. K e e n , l o c . c i t .  11. 12.  J . A . H a r r i s , U n p u b l i s h e d T h e s i s (1922) "The V o l u m e t r i c D e t e r m i n a t i o n o f Z i n c " Pg. 5 (Graph). Z. S. M u k h i n a and M. L . Mironenko-, Z a v a d s k a y a L a b . , 10, 145 - 147, ( 1 9 4 1 ) . ( C . A. 35, 5060, ( 1 9 4 1 ) .  13.  A . W. Thomas, 1 s t E d . , L o n d o n , M c G r a w - H i l l ,  14.  J . A. H a r r i s , L o c . c i t . v - / c f . S n e l l and B i f f e n , C o m m e r c i a l M e t h o d s o f A n a l y s i s , 1 s t E d . , M c G r a w - H i l l , p. 155.  15. 16.  ibid,  30, 904,  (1908).  O s t e r r . Chem. Z t g . , 42, 297-8,  G. W a r i n g ,  (1939).  loc. c i t .  cit.  loc. c i t .  1934, p . 1 7 8 f f ,  S. A. C o l e m a n , G. B. L . S m i t h , I n d . E n g . Chem., A n a l . E d . , 377 - 380, ( 1 9 4 1 ) .  APPENDIX I d e n t i f i c a t i o n of the Mn Fe(CN) 2  Precipitate.  6  Since the p r e c i p i t a t e appeared each time upon the a d d i t i o n of KMn0 t o the K F e ( C N ) 4  4  6  solution, i t  was considered t o be manganese d i o x i d e , manganese f e r r o cyanide, or manganese f e r r l c y a n i d e . Since the t u r b i d i t y produced was not dark and was s o l u b l e i n hot d i l u t e H2SO4, then the formation of both LtaCvj and Mn^ j P a C C N j j T ^  a  r  e  e l i m i n a t e d . Furthermore  MnOg should not form i n an a c i d s o l u t i o n .  Since the  t u r b i d i t y seemed t o appear more r a p i d l y on a l l o w i n g the KMn0 t o l a y e r , then i t was thought perhaps that i t was 4  due t o a h i g h concentration of Mn  . L a t e r work however,  shewed that the p r e c i p i t a t e which formed was due t o an uncommon i o n e f f e c t i n the presence o f the ammonium i o n . A considerable number of s a l t s then were used, f o r example K g S 0 , N a S 0 , NH 4 C1, ( N H ) S 0 , and o t h e r s , and i n each 4  2  4  4  2  4  case the p r e c i p i t a t e was found t o form only when an ammonium s a l t was used. The p r e c i p i t a t e on f i l t r a t i o n appeared a f a i n t grey blue to mauve c o l o r when wet and t h i s i s the c h a r a c t e r i s t i c c o l o r of Mn Fe(CN) . 2  g  The p r e c i p i t a t e was  then washed thoroughly with 50 per cent e t h y l a l c o h o l and dissolved  i n hot very d i l u t e s u l f u r i c a c i d .  On evaporating  the s o l u t i o n i t takes on the b e a u t i f u l l i g h t blue c o l o r  (ii)  that i s c h a r a c t e r i s t i c of the decomposition of f e r r o cyanide, that i s , the formation of Fe [pe(CN)^j » 4  3  The  evaporated s o l u t i o n plus n i t r i c a c i d and sodium b i s muthate gave the d i s t i n c t rose c o l o r f o r Mn0 Ion, 4  thus proving q u a l i t a t i v e l y the p o s i t i v e presence of manganese i n the p r e c i p i t a t e .  Further evidence that  i t must be the ferrocyanide of manganese i s the f a c t that each time the s o l u t i o n cleared up j u s t before the end p o i n t .  Thus the o x i d a t i o n of the ferrocyanide t o  f e r r l c y a n i d e reduced the concentration of Fe(CN)g"  4  ion below the s o l u b i l i t y product of the p r e c i p i t a t e a t the concentration of the manganese i o n present i n the f i n a l solution. On the b a s i s of the q u a l i t a t i v e t e s t s c a r r i e d out above, I considered i t expedient t o t e s t the p r e c i p i t a t e q u a n t i t a t i v e l y f o r I t s composition. The t e s t s applied t o the weighed p r e c i p i t a t e were f i r s t , the exact amount of ferrocyanide present; second, the determination of the exact amount of manganese i n the p r e c i p i t a t e ; and t h i r d , the exact amount of ammonium present.  The p r e c i p i t a t e f o r  a n a l y s i s was prepared i n the f o l l o w i n g r i g o r o u s manner. Pure standard potassium ferrocyanide s o l u t i o n (50 ml.) was d i l u t e d t o 180 ml., 20 ml. of 6N HgS0 and two grams of (NH )gS0 added, and 18 ml* 4  4  4  (iii)  of  s t a n d a r d KMnO, t i t r a t e d  in.  This  solution  was t h e n  stirred  gently  to help  coagulate t h e p r e c i p i t a t e which formed.  solution glass The  and h e a t e d o v e r a b u r n e r t o (50 - 5 5 ) ° C .  was t h e n a l l o w e d  t o stand covered w i t h a watch  f o r one h a l f h o u r t o a l l o w t h e p r e c i p i t a t e  m i x t u r e was f i l t e r e d  p r e c i p i t a t e was t h e n washed t h r e e  distilled sulfuric the  acid  (10 m l . 6N H g S 0  i n a constant  desiccated  Immediately.  4  t o 190 m l . H g O ) .  Each  The G o o c h  acid  through the c r u c i b l e . s t a n d a r d KMn0  4  (20 m l . 6N H S 0 g  small portions  The f i l t r a t e  f o r the available  were a g a i n d r i e d ,  t h e same c o n d i t i o n s  time  crucible exactly  30 m i n u t e s , and w e i g h e d  The p r e c i p i t a t e was t h e n d i s s o l v e d  HgO) b y means o f p o u r i n g  exactly  cold  temperature oven a t  f o r exactly  dilute sulfuric  crucibles  pounds.  w a t e r and t h r e e t i m e s w i t h c o l d v e r y d i l u t e  was t h e n d r i e d  boiling  eight  times with  w a s h i n g was s u c k e d c o m p l e t e l y d r y .  105°C,  to settle.  through a c a r e f u l l y prepared .  Gooch c r u c i b l e under a p r e s s u r e o f e x a c t l y The  The  4  with  t o 180 m l .  of i t repeatedly  was t h e n t i t r a t e d  ferrocyanide.  desiccated  The Gooch  and w e i g h e d  as b e f o r e .  with  under  The d i f f e r e n c e i n  w e i g h t was t h e w e i g h t o f t h e p r e c i p i t a t e d i s s o l v e d .  This  method was u s e d i n p r e f e r e n c e t o t h e method o f f i l t e r i n g the  precipitate  desiccating solving it  t h r o u g h a w e i g h e d Gooch c r u c i b l e ,  and w e i g h i n g t h e p r e c i p i t a t e  and t i t r a t i n g  was f o u n d t h a t  very  f o r available slight  and t h e n  ferrocyanide;  impurities  catalysed  drying, dissince the  (iv) formation of f e r r i c in  the weight o f the p r e c i p i t a t e .  however, f e r r i c dilute the  ferrocyanide  sulfuric acid,  calculated  Is not soluble  error used,  i n the b o i l i n g into  obtained.  titrated available  ferrocyanide  was  i n grams o f F e ( C N ) g ~ ^ and t h i s w e i g h t was u s e d  calculate  the t o t a l weight  forms o f t h e p r e c i p i t a t e . show q u i t e weight.  W i t h t h e method  and t h e r e f o r e d o e s n o t e n t e r  weight' o f t h e p r e c i p i t a t e The  to  f e r r o c y a n i d e w i t h a consequent  of various,  These  most p r o b a b l e ,  w e i g h t s on  comparison  p l a i n l y t h e most c l o s e l y r e l a t e d  A table  o f r e s u l t s below  forms b y  (Table I) i n d i c a t e the  value of these comparisons. TABLE I ( a ) Sample number....  1  A Wt. o f A c t u a l p p t s . 5 Wt. o f F e ( C N ) ~* b y t i t r a t i o n TABLE I Calculated  Sample.,Number .... 2  6  Mn(NH ) Fe(CN) 4  2  MnKgFe(CN)  Mn K  2  Mn K  6  3  6  6  |Fe(CN)  (  le(CN)g.  0.0203 0.01298  3 0.0570 0.0369  0.0664 0.0434  (b)  Weights from B f o r t h e  Following  Mn Fe(CN)  2  2  Forms. 1  2  3  0.0197  0.0561  0.0659  0.0185  0.0528  0.0621  0.0191  0.0544  0.0640  0.0179  0.0512  0.0601  0.0211  0.0601  0.0707  0.0204  0.0581  0.0683  0.0218  0.0621  0.0731  (v)  TABLE I (c) D e v i a t i o n from the Observed for  the F o l l o w i n g Forms.  1  Sample Number .... Mn Fe(CN) 2  6  Mn(NH ) Fe(CN) 4  M n  3  ( N H  2  4 2| )  g  l6]2  e ( G N  Mn(NH ) ge(CN) 4  6  J  2  3  MnKg p ( G N ) g j  -050005  -0.0015  -0,0052  -0.0043  -0.0009  -0.0026  -0.0024  -0.0021  -0.0058  -0.0063  0.0011  0.0031  0.0043  0.0004  0.0011  0.0019  0.0018  0.0051  0.0067  2  An e x a m i n a t i o n the c l o s e s t  3  -0.0009  pe(CN),  g  2  -0.0003  MnKgFefCNjg Mn K  Weights A  o f T a b l e I ( c ) shows  formula b y weight  I s the form  that  Mn Fe(CN)g. 2  Two o t h e r f o r m u l a e , n a m e l y M n K g J F e ( C N ) g J 2 a n d 3  Mn (NH ) 3  4  2  JFe(CN)^j , a r e t o o c l o s e b y weight  comparisons,  g  t o make a d e f i n i t e d e c i s i o n r e g a r d i n g a c t u a l f o r m u l a o f the p r e c i p i t a t e .  F o r t h i s r e a s o n two f u r t h e r  made on t h e p r e c i p i t a t e ; potassium  and the o t h e r a q u a n t i t a t i v e The  in The of  exactly  test  f o r ammonium.  t h e same manner a s d e s c r i b e d p r e v i o u s l y ^ . almost  t o d r y n e s s , 10 m l .  c o n c e n t r a t e d ^ ' H C l added a n d t h e n t h e s o l u t i o n to a paste.  again  The r e s i d u e was t a k e n u p i n 10 m l .  h o t water and t h e f e r r i c  filtered of  test f o r  f e r r o c y a n i d e p r e c i p i t a t e was p r e p a r e d  f i l t r a t e was e v a p o r a t e d  evaporated of  one a q u a l i t a t i v e  t e s t s were  ferrocyanide precipitate  o u t and kept a s i d e f o r f u r t h e r  t h e f i l t r a t e was added 5 m l . o f s o d i u m  # S e e APPENDIX Pp. I i a n d i i i  tests.  To 10 m l .  cobaltinitrite  (vi) solution  (Na Co(N0g) 3  with 3 ml.  The  6  s o l u t i o n was  o f sodium a c e t a t e .  The  allowed  t o s t a n d f o r one h o u r .  formed,  i t was  p o t a s s i u m was  present.  c i p i t a t e used,  f o r 0.2  that  - 0.3  t h e r e w o u l d be The  for  the presence  i t was  examined s p e c t r o s c o p i c a l l y .  The t o be  one  The  6.3  t h u s be  quantitative  test  s u b s t a n c e was  f o r ammonium  was  remedied  vertically  the top o f t h i s , #  Noyes and  some  proved Of  appeared  t o any  lost,  the  precip-  definite  the  by  o f t h e ammonia.  simply placing  After  difficulty  a p h y s i c a l c a r r y over of the  i n the d i s t i l l a t i o n  there  possibility.  o t h e r s were h i g h b e y o n d a l l r e a s o n *  t o be  difficulty condenser  also  formula  correspond  _a c o n s i d e r a b l e amount o f t i m e was  hydroxide  ferric  form of the o r i g i n a l  some.however, d i d n o t  found  chance  o f t h e most d i f f i c u l t . t e s t s , u n d e r t a k e n .  compound and  was  a  spectroscopically  t e n d e t e r m i n a t i o n s t h a t were made f i r s t ,  itate,  i s sensit-  s o l u t i o n was  The  pre-  milligrams  e l i m i n a t e d as a  to correspond to a d e f i n i t e  and  form  out i n the  In neither  of potassium.  can  Fe(CN)  I f the  examined  of potassium.  even a t r a c e  the  S i n c e t h e r e was  the p o t a s s i u m had been f i l t e r e d  found  since  cobalt.lnitri.te. test  m i l l i g r a m s $.  ferrocyanide precipitate  shaken  a p p r e c i a b l e amount o f  w e i g h e d 0.0532 grams, and  of potassium present.  was  precipitate :  This.is.logical,  then  ive  mixture  S i n c e no  assumed t h a t no  then b u f f e r e d  sodium The  a long dry  i n t h e n e c k o f t h e f l a s k and  from  s t e a m was  and  l e d through  a trap  S w i f t , Q u a l . Chem. A n a l . , M a c m i l l a n ,  Pg.  298  (vii) condensed i n a s h o r t c o l d  condenser i n t o  HgSO^ s t a n d a r d  Of f o u r  the  solution.  50 m l . 0.2N  runs u s i n g  s e t up,  maximum w e i g h t o f NH^ f o u n d was 0.0005 grams on a  precipitate  c o n t a i n i n g 0.0309 grams o f F e ( C N ) ~ .  possible  formula for the p r e c i p i t a t e  results  This  4  6  maximum f i g u r e , h o w e v e r , d o e s n o t c o r r e s p o n d  The  this  o f t h i s work s h o w . t h a t  under  t o any  investigation.  the formula cannot he  Mn (NH ) |e(CN) ] . 3  4  2  6  2  The  composition of the ferrocyanide o f  manganese must h e t h e n t h e one o r i g i n a l l y namely M n F e ( C N ) . 2  by  g  the table  ition  below  This conclusion  assumed  Is further  ( T a b l e I I ) a s s u m i n g t h e above  #  established compos-  of the p r e c i p i t a t e . TABLE I I  Weight of p p t  T o t a l wt o f Mn found  0.0450 0.0570 0.0664  0.0154 0.0210 0.0240 The  Wt Mn added (Tit'n)  0.0015 0.0019 0.0023  Difference (Wt Mn in ppt) 0.0139 0.0191 0.0217  w h i c h h a d been, t i t r a t e d  50 m l . o f d i l u t e . n i t r i c  acid  grams o f s o d i u m b i s m u t h a t e a d d e d . boiled  0.0154 0.0195 0.0227  precipitate.  volume o f s t a n d a r d KMnO^ was p l a c e d and  Deviation  -0.0015 -0.0004 -0.0010  manganese was d e t e r m i n e d b y t h e  b i s m u t h a t e method on t h e t i t r a t e d cyanide p r e c i p i t a t e  Calcula t e d wt Mn f r o m £Rt  in.a  The f e r r o -  w i t h a known  conical  flask  ( 1 : 3) a d d e d , t h e n 0.5 The s o l u t i o n  f o r f i v e m i n u t e s and t h e p i n k c o l o r  was  o f the per-  manganate f o r m e d was r e m o v e d . b y t h e d r o p w i s e a d d i t i o n o f # M. D. F r a n c i s , U n p u b l i s h e d T h e s i s , "The D e t ' n o f S m a l l Amounts o f Z i n c i n O r e s "  (viii)  f r e s h l y prepared sodium s u l f i t e .  The oxides of n i t r o g e n  were then removed by vigorous b o i l i n g .  The s o l u t i o n was  cooled w i t h running water to (10 - 15)°C*, 0.5 grams of sodium blsmuthate added, and a f u r t h e r 0.5 gram sample of sodium blsmuthate added to g i v e an excess. mixture was s t i r r e d f o r three minutes.  The  To t h i s s o l u t i o n  was added 50 ml*, of oxide f r e e , three per cent n i t r i c a c i d , and the whole s o l u t i o n f i l t e r e d through a f r e s h l y i g n i t e d Gooch c r u c i b l e .  The f i l t r a t e to which were added  the three per cent n i t r i c a c i d washings was over t i t r a t e d with f e r r o u s ammonium s u l f a t e s o l u t i o n and the excess back t i t r a t e d w i t h standard potassium permanganate.  The  manganese added i n the f e r r o c y a n i d e t i t r a t i o n was then subtracted from the t o t a l manganese determined above* The d i f f e r e n c e was the manganese present i n the p r e c i p i t a t e . Upon reviewing the evidence from both q u a l i t a t i v e and q u a n t i t a t i v e t e s t s presented i n the argument, i t i s evident that the p r e c i p i t a t e must be of the composition MngPetCNjg* the evidence f o r composition*  This i s the c o n c l u s i o n of  BIBLIOGRAPHY Biffen,  P. M.,  "Commercial  Methods o f A n a l y s i s " ,  1 s t Ed.,  M c G r a w - H i l l , p . 155. Coleman, S. A., I n d u s t r i a l E n g i n e e r i n g C h e m i s t r y , Edition, Harris,  377 - 380,  (1941).  J . A., U n p u b l i s h e d T h e s i s ( 1 9 2 2 ) , Determination of Zinc" p. 5  K e e n , W. H., J o u r n a l o f t h e A m e r i c a n 26, Mironenko,  4 - 29,  Analytical  "The V o l u m e t r i c  (Graph).  Chemical  Society",  (1904).  M. L . , Z a v a d s k a y a  L a b o r a t o r y , 1 0 , 145 - 147,  (1941). M u k h i n a , Z. S., Z a v a d s k a y a Sarudi,  L a b o r a t o r y , 10, 145 - 147,  (1941).  I . , O s t e r r C h e m i s c h e n Z e l t u n g , 42, 297 - 298,  (1939).  Seaman, W. H., J o u r n a l o f t h e A m e r i c a n 29-1,  205 - 211,  S n e l l , P. D.,  904,  Society,  (1907).  Stone, E . L., J o u r n a l o f the American 30,  Chemical  Chemical  Society,  (1908).  "Commercial  Methods o f A n a l y s i s " ,  1 s t Ed.,  M c G r a w - H i l l , p . 155. Thomas, A*  W.,  "Colloid  McGraw-Hill, Waring,  C h e m i s t r y " , l3t 1934, p . 1 7 8 f f .  W. G., J o u r n a l o f t h e A m e r i c a n 26,  4 - 29,  Ed., London,  (1904).  Chemical  Society,  

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