﻿Norton 
  — 
  Estimation 
  of 
  Iron 
  in 
  the 
  Ferric 
  State. 
  25 
  

  

  Art. 
  IY. 
  — 
  l^he 
  Estimation 
  of 
  Iron 
  in 
  the 
  Ferine 
  State 
  hy 
  

   Reduction 
  tvith 
  Sodium 
  Thiosidphate 
  and 
  Titration 
  with 
  

   Iodine 
  ; 
  by 
  John 
  T. 
  JN'obton, 
  Jr. 
  

  

  [Contributions 
  from 
  the 
  Kent 
  Chemical 
  Laboratory 
  of 
  Yale 
  University 
  — 
  LXXXIII.] 
  

  

  The 
  action 
  of 
  sodiiim 
  thiosulphate 
  on 
  ferric 
  iron 
  lias 
  long 
  

   been 
  known 
  and 
  depends 
  npon 
  the 
  foUovvdng 
  reaction 
  : 
  

  

  2FeCl3 
  + 
  2Na,S,0^ 
  = 
  2FeC], 
  + 
  ]S^a.,S.p, 
  + 
  2NaCl 
  

  

  As 
  earlj 
  as 
  1859 
  Sherer- 
  proposed 
  a 
  method 
  for 
  the 
  estima- 
  

   tion 
  of 
  ferric 
  iron 
  depending 
  on 
  the 
  above 
  reaction. 
  Sherer's 
  

   method 
  of 
  procednre 
  was 
  to 
  act 
  upon 
  a 
  solution 
  of 
  ferric 
  

   chloride 
  with 
  sodium 
  thiosnlphate 
  until 
  the 
  purple 
  color 
  pro- 
  

   duced 
  by 
  the 
  interaction 
  of 
  these 
  two 
  salts 
  just 
  vanished. 
  

   Mohr's+ 
  experimental 
  tests 
  of 
  this 
  process 
  were 
  not 
  successful. 
  

   A 
  year 
  or 
  two 
  later 
  Kremer 
  and 
  Landolt,:J: 
  after 
  a 
  careful 
  inves- 
  

   tigation 
  of 
  Sherer's 
  process, 
  recommended 
  it 
  with 
  the 
  modifi- 
  

   cation 
  that 
  any 
  free 
  hydrochloric 
  acid 
  present 
  should 
  be 
  

   neutralized 
  by 
  sodium 
  acetate 
  until 
  the 
  solution 
  assumed 
  a 
  red 
  

   color, 
  just 
  enough 
  hydrochloric 
  acid 
  added 
  to 
  destroy 
  this 
  red 
  

   color, 
  and 
  sodium 
  thiosulphate 
  run 
  into 
  the 
  solution 
  in 
  slight 
  

   excess. 
  When 
  the 
  liquid 
  became 
  perfectly 
  colorless 
  and 
  gave 
  

   no 
  reaction 
  for 
  ferric 
  iron 
  with 
  potassium 
  sulphocyanide, 
  the 
  

   excess 
  of 
  sodium 
  thiosulphate 
  was 
  titrated 
  back 
  with 
  iodine 
  

   and 
  starch. 
  The 
  authors 
  also 
  state 
  that 
  the 
  ferric 
  iron 
  should 
  

   not 
  be 
  present 
  in 
  concentrated 
  solution. 
  Very 
  good 
  results 
  

   were 
  claimed 
  for 
  this 
  process, 
  but 
  it 
  apparently 
  gained 
  but 
  

   slight 
  recognition. 
  

  

  Oudemanns,§ 
  who 
  was 
  the 
  next 
  to 
  study 
  the 
  action 
  of 
  ferric 
  

   iron 
  and 
  sodium 
  thiosulphate, 
  claimed 
  that 
  the 
  addition 
  of 
  a 
  

   small 
  quantity 
  of 
  cupric 
  salt 
  to 
  the 
  iron 
  solution 
  hastened 
  the 
  

   reducing 
  action 
  of 
  the 
  sodium 
  thiosulphate. 
  Mohr,|l 
  however, 
  

   condemned 
  this 
  method 
  also 
  as 
  unreliable, 
  both 
  because 
  the 
  

   sodium 
  thiosulphate 
  acted 
  upon 
  the 
  copper 
  as 
  well 
  as 
  the 
  iron 
  

   and 
  also 
  because 
  the 
  potassium 
  sulphocyanide, 
  added 
  as 
  an 
  

   indicator 
  of 
  the 
  completeness 
  of 
  the 
  reduction, 
  produced 
  a 
  

   precipitate 
  of 
  cupric 
  sulphocyanide 
  which 
  interfered 
  with 
  the 
  

   reaction. 
  In 
  a 
  second 
  paper 
  Oudemanns^[ 
  reiterated 
  his 
  former 
  

   statement 
  ,as 
  to 
  the 
  accuracy 
  of 
  his 
  method 
  but 
  advised 
  the 
  use 
  

   of 
  a 
  smaller 
  quantity 
  of 
  the 
  cupric 
  salt. 
  An 
  improvement 
  on 
  

   Oudemanns' 
  process 
  was 
  proposed 
  by 
  Haswell,"^"^ 
  who 
  mixed 
  

  

  *Gelehrle 
  Anzeigen 
  der 
  kdnig. 
  Bajriseh. 
  Acad, 
  vom 
  Auj^. 
  31, 
  1859. 
  

  

  t 
  Anal. 
  d. 
  Chem. 
  u. 
  Pharm.. 
  cxiii, 
  260. 
  % 
  Zeitschr. 
  f. 
  Anal. 
  Chem., 
  i, 
  214. 
  

  

  g 
  ZeitscUr. 
  f. 
  Anal. 
  Chem., 
  vi, 
  129. 
  || 
  Titrirmethode 
  

  

  ^ 
  Zeitschr. 
  f. 
  Anal. 
  Chem., 
  ix, 
  362. 
  

  

  ** 
  Repertorium 
  der 
  Aualvtischen 
  Chem.. 
  i, 
  179. 
  

  

  