﻿Gooch 
  and 
  Walker— 
  -Analysis 
  of 
  Iodides. 
  293 
  

  

  Art. 
  XXYII. 
  — 
  The 
  Application 
  of 
  Iodic 
  Acid 
  to 
  the 
  Analy- 
  

   sis 
  of 
  Iodides 
  ; 
  by 
  F. 
  A. 
  Gooch 
  and 
  C. 
  F. 
  Walker. 
  

  

  [Contributions 
  from 
  the 
  Kent 
  Chemical 
  Laboratory 
  of 
  Tale 
  University. 
  — 
  LXIIL] 
  

  

  It 
  has 
  long 
  been 
  understood 
  that 
  iodic 
  acid 
  is 
  easily 
  and 
  

   completely 
  reduced 
  by 
  an 
  excess 
  of 
  liydriodic 
  acid 
  with 
  the 
  

   liberation 
  of 
  iodine 
  according 
  to 
  the 
  equation 
  : 
  

  

  HI0 
  3 
  + 
  5HI=6l 
  + 
  3H 
  2 
  0. 
  

  

  To 
  apply 
  this 
  reaction 
  to 
  the 
  quantitative 
  estimation 
  of 
  iodic 
  

   acid, 
  it 
  is. 
  only 
  necessary 
  to 
  add 
  to 
  the 
  free 
  iodic 
  acid 
  or 
  solu- 
  

   ble 
  iodate 
  an 
  excess 
  of 
  a 
  soluble 
  iodide, 
  to 
  acidify 
  — 
  best 
  with 
  

   dilute 
  sulphuric 
  acid 
  — 
  and 
  to 
  titrate 
  the 
  iodine 
  thus 
  set 
  free 
  

   with 
  sodium 
  thiosulphate, 
  one-sixth 
  of 
  the 
  iodine 
  found 
  being 
  

   credited 
  to 
  the 
  iodic 
  acid. 
  

  

  It 
  has 
  been 
  shown 
  recently 
  by 
  Riegler* 
  that 
  this 
  reaction 
  

   may 
  be 
  also 
  applied 
  to 
  the 
  quantitative 
  estimation 
  of 
  iodides, 
  

   the 
  iodine 
  set 
  free 
  upon 
  the 
  addition 
  of 
  a 
  known 
  excess 
  of 
  

   iodic 
  acid 
  to 
  the 
  iodide 
  solution 
  being 
  removed 
  by 
  petroleum 
  

   ether, 
  and 
  the 
  residual 
  iodic 
  acid 
  titrated 
  directly 
  with 
  sodium 
  

   thiosulphate. 
  

  

  The 
  present 
  investigation 
  was 
  undertaken 
  to 
  define 
  more 
  

   particularly 
  the 
  limit 
  of 
  applicability 
  of 
  the 
  reaction 
  and 
  to 
  

   establish, 
  if 
  possible, 
  a 
  direct 
  method 
  for 
  the 
  quantitative 
  esti- 
  

   mation 
  of 
  iodides, 
  dependent 
  upon 
  the 
  action 
  of 
  iodic 
  acid 
  or 
  

   an 
  iodate 
  in 
  the 
  presence 
  of 
  free 
  sulphuric 
  acid, 
  neutralization 
  

   of 
  the 
  solution 
  by 
  m^eans 
  of 
  an 
  acid 
  carbonate, 
  and 
  titration 
  of 
  

   the 
  free 
  iodine 
  by 
  arsenious 
  acid 
  — 
  five-sixths 
  of 
  the 
  iodine 
  thus 
  

   found 
  being 
  credited 
  to 
  the 
  iodide 
  to 
  be 
  estimated. 
  It 
  has 
  

   been 
  found 
  that 
  by 
  fulfilling 
  certain 
  necessary 
  conditions, 
  the 
  

   proposed 
  method 
  is 
  entirely 
  successful, 
  so 
  far 
  as 
  concerns 
  the 
  

   estimation 
  of 
  iodine 
  in 
  iodide 
  solutions 
  free 
  from 
  large 
  amounts 
  

   of 
  chlorides 
  as 
  bromides. 
  

  

  In 
  a 
  system 
  containing 
  a 
  considerable 
  quantity 
  of 
  free 
  iodine 
  

   with 
  variable 
  amounts 
  of 
  the 
  other 
  reagents 
  mentioned, 
  as 
  well 
  

   as 
  possible 
  impurities, 
  it 
  is 
  conceivable 
  that 
  secondary 
  reactions 
  

   may 
  occur, 
  depending 
  largely 
  on 
  conditions 
  of 
  mass, 
  time 
  and 
  

   temperature, 
  and 
  of 
  a 
  sort 
  likely 
  to 
  alter 
  the 
  amount 
  of 
  recov- 
  

   erable 
  iodine, 
  or 
  to 
  exert 
  an 
  excessive 
  oxidizing 
  influence 
  on 
  

   the 
  arsenious 
  acid 
  finally 
  titrated. 
  It 
  has 
  been 
  established 
  by 
  

   Schonbein, 
  Lunge 
  and 
  Schoch, 
  and 
  others, 
  that 
  iodine 
  forms 
  

   compounds 
  with 
  the 
  alkalies 
  of 
  the 
  type 
  K-O-I, 
  and 
  Phelpsf 
  

   has 
  recently 
  found 
  that 
  the 
  formation 
  of 
  some 
  such 
  com- 
  

  

  * 
  Zeitschr. 
  fur 
  Anal. 
  Chem., 
  xxxv, 
  305. 
  f 
  This 
  Journal, 
  ii, 
  70, 
  1896. 
  

  

  