﻿28 
  

  

  Norton 
  — 
  Estimation 
  of 
  Iron 
  in 
  the 
  Ferric 
  State. 
  

  

  smaller 
  dilution 
  than 
  400^^™' 
  the 
  decomposing 
  action 
  of 
  the 
  

   acid 
  on 
  the 
  thiosulphate 
  becomes 
  noticeable. 
  When 
  larger 
  

   quantities 
  of 
  iron 
  oxide 
  are 
  dealt 
  with, 
  it 
  appears 
  that 
  the 
  

   dilution 
  ought 
  to 
  be 
  increased 
  proportionally 
  with 
  the 
  quantity 
  

   of 
  ferric 
  oxide 
  present 
  as 
  well 
  as 
  with 
  that 
  of 
  the 
  acid. 
  This 
  

   is 
  illustrated 
  in 
  experiments 
  9-15 
  of 
  the 
  table. 
  On 
  this 
  

   account 
  it 
  seems 
  necessary, 
  assuming 
  that 
  the 
  quantity 
  of 
  acid 
  

   present 
  is 
  always 
  kept 
  within 
  the 
  maximum 
  strength 
  men- 
  

   tioned, 
  1^™^ 
  to 
  400°'"^, 
  to 
  regulate 
  the 
  dilution 
  from 
  the 
  approxi- 
  

   mate 
  quantity 
  of 
  the 
  iron 
  so 
  that 
  not 
  less 
  than 
  400'^'"^ 
  of 
  water 
  

   shall 
  be 
  used 
  to 
  every 
  O'l 
  grm. 
  of 
  iron 
  oxide 
  present. 
  Under 
  

   properly 
  regulated 
  conditions 
  of 
  dilution 
  as 
  regards 
  acid 
  and 
  

   the 
  iron 
  salt, 
  the 
  reduction 
  is 
  completed 
  in 
  from 
  iiv^e 
  to 
  ten 
  

   minutes. 
  

  

  Great 
  excesses 
  of 
  acid, 
  however, 
  contrary 
  to 
  the 
  statement 
  

   of 
  Kremer," 
  retard 
  the 
  reduction 
  greatly, 
  and, 
  in 
  spite 
  of 
  the 
  

   tendency 
  of 
  the 
  thiosulj)hate 
  to 
  decomposition 
  and 
  the 
  produc- 
  

   tion 
  of 
  errors 
  of 
  deficiency 
  under 
  such 
  circumstances, 
  plus 
  

   errors 
  due 
  to 
  partial 
  oxidation 
  come 
  to 
  light. 
  This 
  fact 
  appears 
  

   in 
  the 
  following 
  table, 
  which 
  records 
  the 
  results 
  of 
  processes 
  

   lasting 
  many 
  hours. 
  

  

  

  

  

  Table 
  II. 
  

  

  

  

  

  

  Fe^Os 
  

  

  Fe203 
  

  

  

  

  Na^S-^On 
  

  

  Fe.Oa 
  

  

  

  

  taken. 
  

  

  corrected. 
  

  

  Dilution, 
  

  

  HCl. 
  

  

  in 
  excess. 
  

  

  found. 
  

  

  Error. 
  

  

  

  grms. 
  

  

  grms. 
  

  

  cm^. 
  

  

  cni^. 
  

  

  cm^. 
  

  

  grms. 
  

  

  grms. 
  

  

  18. 
  

  

  •5012 
  

  

  •5002 
  

  

  1700 
  

  

  •10 
  

  

  25^99 
  

  

  5308 
  

  

  •0306-f 
  

  

  19. 
  

  

  •7512 
  

  

  •7497 
  

  

  1200 
  

  

  15 
  

  

  57-8 
  

  

  7685 
  

  

  •01884- 
  

  

  20. 
  

  

  •7520 
  

  

  •7505 
  

  

  2000 
  

  

  15 
  

  

  56^4 
  

  

  7983 
  

  

  •0478-f 
  

  

  21. 
  

  

  •7520 
  

  

  •7505 
  

  

  1700 
  

  

  15 
  

  

  27-2 
  

  

  7627 
  

  

  •0122-f 
  

  

  As 
  to 
  the 
  temperature 
  at 
  which 
  the 
  reduction 
  should 
  be 
  

   made, 
  my 
  experience, 
  contrary 
  to 
  that 
  of 
  Kremer, 
  goes 
  to 
  

   show 
  that 
  no 
  elevation 
  above 
  atmospheric 
  conditions 
  is 
  neces- 
  

   sary 
  ; 
  under 
  the 
  conditions 
  of 
  acidity 
  and 
  dilution 
  laid 
  down, 
  

   the 
  process 
  of 
  reduction 
  is 
  complete 
  within 
  ten 
  minutes 
  after 
  

   the 
  introduction 
  of 
  the 
  thiosulphate 
  ; 
  moreover, 
  former 
  experi- 
  

   encef 
  shows 
  clearly 
  the 
  danger 
  of 
  submitting 
  mixtures 
  of 
  

   sodium 
  thiosulphate 
  and 
  acid 
  to 
  temperatures 
  much 
  above 
  the 
  

   ordinary. 
  On 
  the 
  other 
  hand, 
  artificial 
  reduction 
  of 
  tempera- 
  

   ture 
  tends 
  to 
  retard 
  the 
  action 
  to 
  an 
  impossible 
  degree. 
  Thus, 
  

   in 
  an 
  experiment 
  it 
  took 
  five 
  minutes 
  to 
  reduce 
  0-0500 
  of 
  ferric 
  

   oxide 
  at 
  21° 
  C. 
  completely 
  at 
  a 
  dilution 
  of 
  200'"'' 
  and 
  in 
  the 
  

   presence 
  of 
  y^^^ 
  of 
  hydrochloric 
  acid 
  ; 
  under 
  conditions 
  other- 
  

   wise 
  precisely 
  similar 
  excepting 
  that 
  the 
  temperature 
  was 
  low- 
  

   ered 
  to 
  0° 
  C, 
  the 
  action 
  lingered 
  forty-five 
  minutes. 
  

  

  Zeit. 
  f. 
  Anal. 
  Chem., 
  i, 
  214. 
  

  

  f 
  This 
  Journal, 
  vol. 
  vii, 
  287. 
  

  

  