﻿128 
  Z. 
  C. 
  Jones 
  — 
  An 
  lodoraetric 
  Method 
  for 
  the 
  

  

  potassium 
  iodide 
  and 
  iodate, 
  proportionately 
  to 
  the 
  time 
  

   required 
  for 
  the 
  liberation, 
  is 
  taken 
  as 
  a 
  measure 
  of 
  the 
  streno^ths 
  

   of 
  the 
  acids 
  developed. 
  

  

  Equal 
  amounts 
  (10^™^) 
  of 
  a 
  standard 
  solution 
  of 
  boric 
  acid, 
  

   prepared 
  from 
  the 
  anhydride,* 
  were 
  drawn 
  into 
  separate 
  

   Erlenmeyer 
  flasks 
  and 
  a 
  neutral 
  solution 
  of 
  iodide 
  and 
  iodate 
  

   added 
  to 
  each 
  in 
  an 
  amount 
  sufficient 
  to 
  liberate 
  iodine 
  in 
  

   quantities 
  corresponding 
  to 
  the 
  acid 
  used. 
  One 
  solution 
  was 
  

   treated 
  with 
  glycerine 
  enough 
  to 
  constitute 
  one-half 
  the 
  entire 
  

   volume 
  of 
  the 
  liquid 
  : 
  mannite 
  (about 
  5 
  grms.) 
  was 
  added 
  to 
  

   the 
  other. 
  The 
  thiosulphate 
  required, 
  immediately 
  and 
  after 
  

   definite 
  periods 
  of 
  time, 
  is 
  shown 
  for 
  each 
  solution 
  in 
  the 
  fol- 
  

   lowing 
  table 
  : 
  

  

  Table 
  I. 
  

  

  B2O3 
  solution 
  (10«"^3) 
  ;B^^03 
  solution 
  (10<=°>3) 
  

  

  with 
  maunite. 
  with 
  glycerine. 
  

  

  Thiosulphate 
  required. 
  Time. 
  Thiosulphate 
  required. 
  

  

  18-60^°^' 
  immediately 
  8-48^'"' 
  

  

  21-30 
  " 
  after 
  15 
  minutes 
  lO'oO 
  " 
  

  

  22-00 
  " 
  " 
  30 
  " 
  11-15 
  " 
  

  

  22-05'' 
  " 
  2 
  hours. 
  11-60" 
  

  

  The 
  solution 
  of 
  boric 
  acid 
  contained 
  T"706 
  grm. 
  per 
  liter. 
  

   The 
  thiosulphate 
  was 
  -0999 
  normal. 
  According 
  to 
  theory, 
  the 
  

   amount 
  of 
  thiosulphate 
  required 
  for 
  10*^"'^ 
  of 
  the 
  boric 
  acid 
  

   solution 
  is 
  22*02^"'^ 
  From 
  these 
  data 
  we 
  may 
  observe 
  that 
  at 
  

   the 
  end 
  of 
  30 
  minutes, 
  in 
  the 
  solution 
  containing 
  mannite, 
  

   practically 
  the 
  theoretical 
  amount 
  of 
  thiosulphate 
  had 
  been 
  

   used, 
  while 
  only 
  about 
  50 
  per 
  cent 
  of 
  that 
  amount 
  had 
  been 
  

   required 
  to 
  bleach 
  the 
  iodine 
  liberated 
  by 
  the 
  glycerine 
  com- 
  

   pound. 
  Obviously, 
  mannite 
  forms 
  with 
  boric 
  acid 
  a 
  more 
  

   acidic 
  compound 
  than 
  glycerine, 
  and, 
  from 
  the 
  indication 
  given 
  

   in 
  the 
  above 
  experiments, 
  may 
  be 
  relied 
  upon, 
  under 
  certain 
  

   conditions, 
  to 
  liberate 
  the 
  theoretical 
  amount 
  of 
  iodine. 
  If, 
  

   from 
  the 
  iodide 
  and 
  iodate 
  used 
  to 
  destroy 
  the 
  excess 
  of 
  min- 
  

   eral 
  acid 
  and 
  already 
  present, 
  the 
  boric 
  acid, 
  upon 
  the 
  addition 
  

   of 
  mannite 
  does 
  liberate 
  iodine 
  regularly 
  — 
  as 
  the 
  previous 
  

   experiments 
  seem 
  to 
  indicate 
  — 
  this 
  liberated 
  iodine 
  should 
  

   form 
  a 
  most 
  convenient 
  measure 
  of 
  the 
  boric 
  acid 
  present. 
  

  

  On 
  studying 
  the 
  conditions 
  requisite 
  for 
  the 
  complete 
  libera- 
  

   tion 
  of 
  iodine 
  according 
  to 
  theory, 
  several 
  important 
  points 
  

   have 
  come 
  to 
  light. 
  

  

  It 
  has 
  not 
  been 
  found 
  possible 
  under 
  any 
  conditions 
  to 
  rely 
  

   upon 
  the 
  immediate 
  liberation 
  of 
  the 
  full 
  amount 
  of 
  iodine 
  : 
  a 
  

  

  *The 
  recrystnllized 
  hydrous 
  boric 
  acid 
  should 
  be 
  fused 
  in 
  a 
  platinum 
  dish 
  and, 
  

   after 
  cooling 
  and 
  breaking 
  into 
  small 
  pieces, 
  the 
  desired 
  amount 
  placed 
  in 
  a 
  small 
  

   weighed 
  phitiuum 
  crucible 
  and 
  again 
  fused 
  until 
  no 
  more 
  water 
  escapes. 
  After 
  

   cooling 
  and 
  weighing, 
  the 
  boric 
  oxide 
  may 
  be 
  separated 
  from 
  the 
  crucible, 
  or 
  with 
  

   it 
  placed 
  in 
  warm 
  water, 
  dissolved 
  and 
  made 
  up 
  to 
  a 
  definite 
  volume. 
  

  

  