﻿Norton 
  — 
  Estimation 
  of 
  Iron 
  in 
  the 
  Ferric 
  State. 
  

  

  29 
  

  

  Lastly, 
  the 
  question 
  as 
  to 
  the 
  excess 
  of 
  thiosiilphate 
  neces- 
  

   sary 
  to 
  complete 
  the 
  reduction 
  within 
  a 
  reasonable 
  time 
  must 
  

   be 
  considered. 
  In 
  nearly 
  all 
  previously 
  recorded 
  experi- 
  

   ments 
  the 
  excess 
  of 
  thiosulphate 
  was 
  not 
  less 
  than 
  15^°^^ 
  of 
  the 
  

  

  IV 
  

  

  10 
  

  

  solution. 
  

  

  The 
  fol 
  

  

  lowing 
  t 
  

  

  able 
  s] 
  

  

  lows 
  the 
  e 
  

  

  effect 
  of 
  

  

  diminish- 
  

  

  ing 
  

  

  this 
  excess. 
  

  

  

  

  

  

  

  

  

  

  Table 
  III. 
  

  

  

  

  

  

  FesOs 
  

  

  FeoOa 
  

  

  

  

  NaoSsOs 
  

  

  Fe^Os 
  

  

  

  

  taken. 
  

  

  corrected. 
  

  

  Dilution. 
  

  

  HCl. 
  

  

  in 
  excess. 
  

  

  found. 
  

  

  Brror. 
  

  

  

  grms. 
  

  

  grms. 
  

  

  cm^. 
  

  

  cm 
  3. 
  

  

  cm 
  3. 
  

  

  grms. 
  

  

  grms. 
  

  

  22. 
  

  

  •0250 
  

  

  •0250 
  

  

  400 
  

  

  i 
  

  

  ' 
  12-2 
  

  

  •0241 
  

  

  •0009 
  — 
  

  

  23. 
  

  

  •0500 
  

  

  •0499 
  

  

  400 
  

  

  i 
  

  

  12-2 
  

  

  •0495 
  

  

  •0004- 
  

  

  24. 
  

  

  •0500 
  

  

  •0499 
  

  

  400 
  

  

  i 
  

  

  13-66 
  

  

  •0493 
  

  

  •0006- 
  

  

  25. 
  

  

  •1000 
  

  

  •0998 
  

  

  400 
  

  

  1 
  

  

  7-31 
  

  

  •0984 
  

  

  •0014 
  — 
  

  

  26. 
  

  

  •1000 
  

  

  •0998 
  

  

  400 
  

  

  1 
  

  

  7-63 
  

  

  •0972 
  

  

  •0026- 
  

  

  27. 
  

  

  •1001 
  

  

  •0999 
  

  

  400 
  

  

  1 
  

  

  12^88 
  

  

  •1007 
  

  

  •0008-1- 
  

  

  28. 
  

  

  ♦1498 
  

  

  •1495 
  

  

  600 
  

  

  u 
  

  

  11^97 
  

  

  •1475 
  

  

  •0020- 
  

  

  29. 
  

  

  •1996 
  

  

  •1992 
  

  

  800 
  

  

  2 
  

  

  12^43 
  

  

  •1980 
  

  

  •0012- 
  

  

  From 
  the 
  above 
  experiments 
  taken 
  in 
  connection 
  with 
  those 
  

   of 
  Table 
  I 
  it 
  is 
  clear 
  that 
  there 
  should 
  always 
  be 
  present 
  an 
  

  

  n 
  

   excess 
  of 
  at 
  least 
  IS'^"'^ 
  of 
  the 
  -— 
  solution 
  of 
  sodium 
  thiosul- 
  

   phate. 
  If 
  the 
  quantity 
  of 
  hydrochloric 
  acid 
  is 
  kept 
  very 
  low 
  

   there 
  is 
  no 
  reason 
  why 
  this 
  excess 
  of 
  thiosulphate 
  could 
  not 
  be 
  

   considerable 
  without 
  producing 
  any 
  disturbing 
  effect. 
  Prac- 
  

   tically, 
  however, 
  the 
  presence 
  of 
  an 
  excess 
  between 
  the 
  limits 
  

  

  of 
  15^"'^ 
  and 
  35^°"^ 
  of 
  the 
  — 
  solution 
  has 
  been 
  found 
  to 
  give 
  

  

  the 
  most 
  satisfactory 
  results. 
  

  

  To 
  recapitulate 
  then, 
  it 
  has 
  been 
  shown 
  that 
  the 
  dilution 
  

   must 
  be 
  at 
  least 
  ttOO^""^ 
  for 
  each 
  •I 
  of 
  a 
  grm. 
  of 
  iron 
  oxide 
  pres- 
  

   ent, 
  that 
  the 
  quantity 
  of 
  acid 
  should 
  never 
  exceed 
  1^™^ 
  of 
  the 
  

   strong 
  acid 
  to 
  each 
  400°™^ 
  of 
  water, 
  that 
  the 
  time 
  of 
  reduction 
  

   must 
  be 
  short 
  to 
  avoid 
  progressive 
  oxidation, 
  that 
  the 
  tempera- 
  

   ture 
  of 
  the 
  solution 
  should 
  be 
  kept 
  at 
  the 
  normal 
  temperature 
  

   of 
  the 
  atmosphere, 
  and 
  finally 
  that 
  the 
  excess 
  of 
  sodium 
  thio- 
  

   sulphate 
  present 
  should 
  never 
  be 
  less 
  than 
  lo"^"'^ 
  of 
  the 
  — 
  solu- 
  

   tion. 
  In 
  the 
  case 
  of 
  large 
  dilution 
  the 
  use 
  of 
  freshly 
  boiled 
  

   water 
  is 
  recommended 
  so 
  as 
  to 
  avoid 
  the 
  reoxidizing 
  effect 
  of 
  

   the 
  air 
  upon 
  the 
  reduced 
  iron. 
  In 
  the 
  experiments 
  included 
  

   in 
  the 
  following 
  table, 
  the 
  above 
  precautions 
  were 
  closely 
  ad- 
  

   hered 
  to 
  and 
  manifestly 
  satisfactory 
  results 
  were 
  obtained. 
  

  

  