﻿240 
  Gooch 
  — 
  Estimation 
  of 
  Molybdenum 
  lodometrically 
  . 
  

  

  obtained 
  by 
  their 
  unmodified 
  method 
  have 
  been 
  even 
  worse 
  

   than 
  their 
  own. 
  

  

  In 
  another 
  series 
  of 
  six 
  determinations, 
  in 
  which 
  molybde- 
  

   num 
  trioxide 
  was 
  the 
  starting 
  point, 
  Friedheim 
  and 
  Euler 
  

   were 
  more 
  successful, 
  the 
  errors 
  varying 
  from 
  0*0006 
  grm. 
  + 
  

   to 
  0*0006 
  grm. 
  — 
  . 
  Thus 
  Friedheim 
  and 
  Euler 
  establish 
  by 
  

   their 
  own 
  results 
  the 
  fact 
  that 
  the 
  hitting 
  of 
  the 
  right 
  point 
  at 
  

   which 
  to 
  stop 
  their 
  process 
  of 
  boiling 
  is 
  a 
  matter 
  of 
  chance. 
  

   In 
  spite 
  of 
  the 
  probability 
  that 
  some 
  of 
  the 
  iodine 
  which 
  they 
  

   found 
  in 
  the 
  receiver 
  was 
  liberated 
  by 
  atmospheric 
  action, 
  the 
  

   fact 
  remains 
  that 
  their 
  results 
  are 
  in 
  many 
  cases 
  very 
  low. 
  

   That 
  is, 
  they 
  did 
  not 
  boil 
  long 
  enough. 
  

  

  The 
  difficulty 
  appears 
  again 
  in 
  the 
  modification 
  of 
  their 
  

   method 
  which 
  Friedheim 
  and 
  Euler 
  apply 
  to 
  the 
  determination 
  

   of 
  molydennm 
  trioxide 
  associated 
  with 
  vanadium 
  pentoxide*, 
  

   namely, 
  the 
  distillation 
  with 
  phosphoric 
  acid 
  and 
  potassium 
  

   iodide 
  of 
  the 
  residue 
  left 
  after 
  reducing 
  the 
  vanadium 
  pentox- 
  

   ide 
  by 
  hydrochloric 
  acid 
  and 
  potassium 
  bromide, 
  according 
  to 
  

   the 
  method 
  of 
  Holverscheit. 
  We 
  reproduce 
  the 
  part 
  of 
  their 
  

   table 
  which 
  refers 
  to 
  the 
  determination 
  of 
  the 
  molybdenum, 
  

   adding, 
  however, 
  columns 
  containing 
  the 
  errors 
  and 
  corrected 
  

   percentages. 
  

  

  

  

  Per 
  cent 
  

  

  

  Per 
  cent 
  

  

  MoO, 
  

  

  MoO 
  3 
  

  

  Mo0 
  3 
  

  

  Error. 
  

  

  Mo0 
  5 
  . 
  

  

  taken. 
  

  

  found. 
  

  

  F. 
  and 
  E. 
  

  

  grm. 
  

  

  Recalculated. 
  

  

  0*15037 
  

  

  0*15005 
  

  

  99-79 
  

  

  0*00032 
  — 
  

  

  ' 
  99-79 
  

  

  0*16895 
  

  

  0*16879 
  

  

  99-90 
  

  

  0*00016 
  — 
  

  

  99*90 
  

  

  0-17758 
  

  

  0*17729 
  

  

  99-84 
  

  

  0*00029 
  — 
  

  

  99*84 
  

  

  0*24975 
  

  

  0-24962 
  

  

  99-95 
  

  

  0-00013 
  — 
  

  

  9995 
  

  

  0*33151 
  

  

  0-33607 
  

  

  [99*87] 
  

  

  0*00456 
  + 
  

  

  101-38 
  

  

  Four 
  of 
  the 
  five 
  determinations 
  are 
  accurate, 
  but 
  the 
  fact 
  

   that 
  all 
  figures 
  are 
  carried 
  out 
  to 
  the 
  fifth 
  decimal 
  place 
  does 
  

   not 
  keep 
  three 
  good 
  sized 
  figures 
  out 
  of 
  the 
  error 
  column 
  for 
  

   the 
  fifth 
  determination. 
  

  

  It 
  is 
  hardly 
  necessary, 
  in 
  the 
  light 
  of 
  a 
  comparison 
  of 
  the 
  

   results 
  of 
  Friedheim 
  and 
  Euler 
  with 
  ours, 
  to 
  discuss 
  further 
  

   the 
  unreliability 
  of 
  the 
  unmodified 
  process. 
  The 
  necessity 
  of 
  

   a 
  proper 
  control 
  of 
  the 
  volume, 
  strength 
  of 
  acid, 
  and 
  excess 
  of 
  

   potassium 
  iodide, 
  as 
  well 
  as 
  proper 
  protection 
  from 
  atmos- 
  

   pheric 
  oxidation, 
  is 
  real. 
  

  

  On 
  a 
  former 
  occasion 
  the 
  unpleasant 
  necessity 
  presented 
  

   itselff 
  of 
  pointing 
  out 
  the 
  fact 
  that 
  certain 
  unfounded 
  criti- 
  

   cisms 
  on 
  the 
  part 
  of 
  Friedheim 
  and 
  Meyer 
  were 
  based 
  upon 
  an 
  

   unfortunate 
  use 
  by 
  them 
  of 
  impure 
  reagents 
  ; 
  the 
  difficulty 
  in 
  

   the 
  present 
  case, 
  for 
  Friedheim 
  and 
  Euler, 
  seems 
  to 
  reside 
  in 
  

   the 
  arithmetical 
  process. 
  

  

  * 
  Ber. 
  d. 
  d. 
  Chem. 
  Gesell., 
  xzviii, 
  2072. 
  

  

  f 
  Gooch 
  and 
  Browning, 
  this 
  Journal, 
  xlv, 
  334. 
  

  

  