﻿Acid 
  in 
  jpresence 
  of 
  Haloid 
  Salts. 
  125 
  

  

  oxalic 
  acid 
  does 
  not 
  suffice 
  to 
  reconvert 
  it. 
  In 
  the 
  presence 
  of 
  

   an 
  excess 
  of 
  potassium 
  iodide 
  the 
  higher 
  manganic 
  compounds 
  

   are 
  completely 
  reduced 
  with 
  rapidity 
  and 
  the 
  iodine 
  liberated 
  

   is 
  the 
  measure 
  of 
  the 
  excess 
  of 
  permanganate 
  over 
  that 
  

   required 
  to 
  oxidize 
  the 
  tellurous 
  acid 
  ; 
  the 
  difference 
  between 
  

   the 
  amount 
  of 
  permanganate 
  thus 
  indicated 
  and 
  that 
  originally 
  

   introduced 
  should 
  determine 
  the 
  amount 
  of 
  the 
  tellurous 
  acid. 
  

   It 
  is 
  upon 
  this 
  basis 
  that 
  ^N'orris 
  and 
  Fay^ 
  have 
  founded 
  their 
  

   excellent 
  iodometric 
  determination 
  of 
  tellurous 
  acid. 
  This 
  

   process 
  consists 
  in 
  treating 
  the 
  alkaline 
  solution 
  of 
  tellurous 
  

   acid 
  with 
  standard 
  permanganate 
  until 
  the 
  meniscus 
  of 
  the 
  

   liquid 
  shows 
  a 
  deep 
  pink 
  color, 
  then 
  diluting 
  the 
  solution 
  with 
  

   ice-water, 
  adding 
  potassium 
  iodide 
  and 
  sulphuric 
  acid, 
  and 
  

   titrating 
  with 
  sodium 
  thiosulphate. 
  The 
  results 
  are 
  excellent. 
  

   It 
  is 
  plain 
  that 
  any 
  agent 
  capable 
  of 
  converting 
  the 
  iodine 
  

   to 
  hydriodic 
  acid 
  without 
  at 
  the 
  same 
  time 
  reducing 
  telluric 
  

   acid 
  should 
  be 
  capable 
  of 
  measuring 
  the 
  excess 
  of 
  the 
  perman- 
  

   ganate, 
  and 
  so 
  the 
  amount 
  of 
  tellurous 
  acid 
  originally 
  present. 
  

   We 
  find 
  that 
  the 
  standard 
  arsenite 
  made, 
  as 
  usual, 
  by 
  dissolv- 
  

   ing 
  4-95 
  grams 
  of 
  pure 
  resublimed 
  arsenious 
  oxide 
  to 
  the 
  liter 
  

   of 
  water 
  containing 
  potassium 
  bicarbonate 
  answers 
  the 
  purpose 
  

   admirably, 
  and 
  possesses 
  the 
  further 
  advantage 
  of 
  fixing 
  at 
  

   once 
  the 
  entire 
  standard 
  of 
  the 
  process, 
  the 
  strength 
  of 
  the 
  

  

  permanganate 
  (approximately 
  — 
  ) 
  being 
  determined 
  by 
  run- 
  

   ning 
  a 
  definite 
  volume 
  of 
  its 
  solution 
  into 
  water 
  containing 
  

   potassium 
  iodide 
  (I 
  gram) 
  with 
  2 
  to 
  3^""^ 
  of 
  dilute 
  sulphuric 
  

   acid 
  and 
  titrating 
  by 
  the 
  standard 
  arsenite 
  the 
  iodine 
  (set 
  

   free 
  by 
  the 
  action 
  of 
  the 
  excess 
  of 
  permanganate 
  and 
  higher 
  

   oxides) 
  after 
  neutralization 
  with 
  acid 
  potassium 
  bicarbonate. 
  

   In 
  this 
  titration 
  of 
  iodine 
  by 
  the 
  arsenite 
  we 
  find 
  it 
  best 
  to 
  dis- 
  

   pense 
  with 
  the 
  starch 
  solution 
  usually 
  employed 
  to 
  secure 
  the 
  

   end 
  reaction. 
  The 
  color 
  of 
  the 
  free 
  iodine 
  itself 
  is 
  sufficiently 
  

   definite, 
  even 
  at 
  a 
  dilution 
  so 
  much 
  as 
  300^""^, 
  and 
  its 
  disap- 
  

   pearance 
  under 
  the 
  action 
  of 
  the 
  arsenite 
  is 
  much 
  sharper 
  than 
  

   that 
  of 
  the 
  blue 
  starch 
  iodide. 
  

  

  In 
  Table 
  III 
  are 
  recorded 
  results 
  obtained 
  by 
  adding 
  the 
  

   alkaline 
  solution 
  of 
  tellurous 
  oxide 
  to 
  100^"^' 
  of 
  water 
  contain- 
  

   ing 
  0'5 
  gram 
  or 
  1 
  gram 
  of 
  potassium 
  iodide, 
  introducing 
  the 
  

   standardized 
  potassium 
  permanganate 
  until 
  the 
  green 
  color 
  of 
  

  

  the 
  manganate 
  appears 
  (about 
  30"^"'^ 
  of 
  the 
  — 
  solution 
  for 
  

  

  every 
  O'l 
  gram 
  of 
  TeO^), 
  adding 
  a 
  few 
  cubic 
  centimeters 
  of 
  

   dilute 
  sulphuric 
  acid 
  followed, 
  when 
  the 
  solution 
  has 
  cleared 
  

   and 
  separated 
  iodine, 
  by 
  an 
  excess 
  of 
  acid 
  potassium 
  carbonate, 
  

  

  * 
  Am. 
  Chem. 
  Jour., 
  xx, 
  278. 
  

  

  