﻿Norton 
  — 
  Estimation 
  of 
  Iron 
  in 
  the 
  Ferric 
  State. 
  27 
  

  

  siilphocjanide 
  added 
  to 
  serve 
  as 
  an 
  indicator 
  and 
  an 
  excess 
  of 
  

   sodium 
  thiosulphate 
  was 
  run 
  in 
  until, 
  after 
  standing 
  for 
  a 
  few- 
  

   minutes, 
  the 
  solution 
  became 
  perfectly 
  colorless, 
  and 
  the 
  excess 
  

   of 
  sodium 
  thiosulphate 
  was 
  then 
  titrated 
  back 
  with 
  decinormal 
  

   iodine 
  after 
  the 
  addition 
  of 
  starch. 
  

  

  Several 
  sources 
  of 
  error 
  are, 
  plainly, 
  possible 
  in 
  the 
  process 
  : 
  

   incompleteness 
  in 
  the 
  reduction 
  of 
  the 
  ferric 
  salt; 
  decomposi- 
  

   tion 
  of 
  the 
  thiosulphate 
  by 
  the 
  acid, 
  resulting 
  in 
  the 
  subse- 
  

   quent 
  over-run 
  of 
  iodine 
  ; 
  the 
  possible 
  tendency 
  of 
  the 
  ferric 
  

   salt 
  under 
  concentration 
  to 
  oxidize 
  the 
  thiosulphate 
  to 
  the 
  con- 
  

   dition 
  of 
  the 
  sulphate 
  rather 
  than 
  to 
  that 
  of 
  the 
  tetrathionate 
  ; 
  

   and 
  finally 
  the 
  oxidizing 
  action 
  of 
  the 
  air, 
  which 
  may 
  tend 
  to 
  

   keep 
  up 
  progressive 
  oxidation 
  of 
  the 
  iron 
  salt 
  and 
  excessive 
  

   expenditures 
  of 
  thiosulphate. 
  The 
  lirst 
  three 
  sources 
  of 
  diffi- 
  

   culty 
  tend 
  to 
  produce 
  errors 
  of 
  deficiency 
  ; 
  the 
  fourth 
  an 
  error 
  

   of 
  excess. 
  

  

  The 
  first 
  step 
  in 
  the 
  experimental 
  study 
  of 
  the 
  process 
  was 
  

   to 
  determine 
  the 
  effect 
  of 
  varying 
  dilution 
  upon 
  the 
  estima- 
  

   tion 
  of 
  a 
  given 
  quantity 
  of 
  iron 
  reduced 
  by 
  sodium 
  thiosulphate, 
  

   taken 
  in 
  practically 
  uniform 
  excess 
  above 
  the 
  amount 
  theo- 
  

   retically 
  required, 
  in 
  the 
  presence 
  of 
  1™^^ 
  of 
  hydrochloric 
  acid. 
  

  

  

  

  

  

  Table 
  I. 
  

  

  

  

  

  

  FeoOs 
  

  

  FeoOa 
  

  

  

  

  NaoSoOs 
  

  

  Fe,03 
  

  

  

  

  taken. 
  

  

  corrected. 
  

  

  Dilution 
  

  

  HCl. 
  

  

  in 
  excess. 
  

  

  found. 
  

  

  Error. 
  

  

  

  grms. 
  

  

  grms. 
  

  

  cm^. 
  

  

  cm^ 
  

  

  cm^. 
  

  

  grms. 
  

  

  grms. 
  

  

  1. 
  

  

  •1000 
  

  

  •0998 
  

  

  100 
  

  

  1 
  

  

  18-08 
  

  

  •0957 
  

  

  •0041- 
  

  

  2. 
  

  

  •1000 
  

  

  •0998 
  

  

  200 
  

  

  1 
  

  

  20 
  

  

  -0966 
  

  

  •0032 
  — 
  

  

  3. 
  

  

  •1000 
  

  

  •0998 
  

  

  300 
  

  

  1 
  

  

  17 
  •56 
  

  

  -0995 
  

  

  •0003 
  — 
  

  

  4. 
  

  

  •1000 
  

  

  •0998 
  

  

  400 
  

  

  1 
  

  

  17-16 
  

  

  •0998 
  

  

  •0000 
  

  

  5. 
  

  

  •1000 
  

  

  •0998 
  

  

  600 
  

  

  1 
  

  

  17-76 
  

  

  •0996 
  

  

  •0002- 
  

  

  6. 
  

  

  •1000 
  

  

  •0998 
  

  

  800 
  

  

  1 
  

  

  17-65 
  

  

  •0993 
  

  

  •0005 
  — 
  

  

  /. 
  

  

  •1000 
  

  

  •0998 
  

  

  1000 
  

  

  1 
  

  

  18-02 
  

  

  •0988 
  

  

  •0010 
  — 
  

  

  8. 
  

  

  •1000 
  

  

  •0998 
  

  

  1200 
  

  

  1 
  

  

  17-95 
  

  

  •0977 
  

  

  •0021 
  — 
  

  

  9. 
  

  

  •1000 
  

  

  •0998 
  

  

  1400 
  

  

  1 
  

  

  17-99 
  

  

  •0965 
  

  

  •0033- 
  

  

  10. 
  

  

  .1000 
  

  

  •0998 
  

  

  1600 
  

  

  1 
  

  

  18-01 
  

  

  •0947 
  

  

  •0051- 
  

  

  11. 
  

  

  •2001 
  

  

  •1997 
  

  

  400 
  

  

  2 
  

  

  27-05 
  

  

  •2029 
  

  

  •0032 
  + 
  

  

  12. 
  

  

  •2001 
  

  

  •1997 
  

  

  800 
  

  

  2 
  

  

  15-95 
  

  

  •1998 
  

  

  •0001 
  + 
  

  

  13. 
  

  

  •4998 
  

  

  •4988 
  

  

  1000 
  

  

  2 
  

  

  22^36 
  

  

  •5104 
  

  

  •0126-F 
  

  

  14. 
  

  

  •5051 
  

  

  •5041 
  

  

  1800 
  

  

  4 
  

  

  15-27 
  

  

  •5026 
  

  

  '0017 
  — 
  

  

  15. 
  

  

  •4002 
  

  

  •3994 
  

  

  1500 
  

  

  4 
  

  

  27-29 
  

  

  •3996 
  

  

  •0002 
  + 
  

  

  16. 
  

  

  •V502 
  

  

  •7487 
  

  

  1000 
  

  

  1 
  

  

  9-73 
  

  

  •7572 
  

  

  •0085 
  + 
  

  

  17. 
  

  

  •7029 
  

  

  •7015 
  

  

  2000 
  

  

  4 
  

  

  12-67 
  

  

  •7004 
  

  

  •0011- 
  

  

  This 
  table 
  shows 
  plainly 
  that 
  with 
  quantities 
  of 
  ferric 
  oxide 
  

   present 
  np 
  to 
  ()•! 
  grm. 
  the 
  dilution 
  can 
  vary 
  from 
  400^""' 
  to 
  

   j[QQQcm3 
  i^j. 
  g^^^i^ 
  ^^^^3 
  ^£ 
  strong 
  hydrochloric 
  acid 
  and 
  still 
  give 
  

   excellent 
  results. 
  At 
  a 
  dilution 
  greater 
  than 
  1000"^' 
  the 
  

   action 
  of 
  the 
  thiosulphate 
  is 
  evidently 
  incomplete, 
  and 
  at 
  a 
  

  

  