﻿238 
  Gooch 
  — 
  Estimation 
  of 
  Molybdenum 
  Iodometrically. 
  

  

  start 
  the 
  distillation 
  with 
  a 
  definite 
  volume 
  (40 
  cm3 
  ) 
  of 
  liquid 
  

   and 
  boil 
  until 
  a 
  definite 
  volume 
  (25 
  cm3 
  ) 
  was 
  reached, 
  care 
  being 
  

   taken 
  with 
  regard 
  to 
  the 
  strength 
  of 
  acid 
  and 
  the 
  excess 
  of 
  

   potassium 
  iodide 
  employed. 
  Experience 
  showed 
  unmistakably 
  

   that 
  in 
  order 
  to 
  avoid 
  the 
  decomposing 
  action 
  of 
  the 
  air 
  upon 
  

   the 
  hot 
  vaporous 
  hydriodic 
  acid 
  in 
  the 
  retort, 
  it 
  was 
  necessary 
  

   to 
  go 
  beyond 
  the 
  measures 
  advised 
  by 
  Friedbeim 
  and 
  Euler 
  

   (namely, 
  to 
  warm 
  the 
  retort 
  and 
  its 
  contents 
  slowly, 
  heating 
  to 
  

   boiling 
  only 
  when 
  the 
  connecting 
  tube 
  was 
  well 
  filled 
  with 
  

   iodine 
  vapor 
  and 
  the 
  tendency 
  toward 
  back-suction 
  of 
  the 
  liquid 
  

   in 
  the 
  receiver 
  began 
  to 
  appear) 
  and 
  to 
  conduct 
  the 
  operation 
  in 
  

   a 
  simple 
  little 
  apparatus 
  (the 
  retort 
  holding 
  about 
  100 
  cm3 
  ) 
  put 
  

   together 
  entirely 
  with 
  sealed 
  and 
  ground 
  joints, 
  as 
  shown 
  in 
  

   the 
  figure 
  of 
  the 
  former 
  paper, 
  so 
  arranged 
  that 
  a 
  current 
  of 
  

   purified 
  carbon 
  dioxide 
  could 
  be 
  passed 
  through 
  retort 
  and 
  

   receiver 
  during 
  the 
  distillation. 
  With 
  this 
  apparatus 
  we 
  were 
  

   able 
  to 
  determine 
  with 
  accuracy 
  the 
  point 
  of 
  concentration 
  

   at 
  which 
  the 
  free 
  iodine 
  left 
  the 
  liquid, 
  the 
  molybdic 
  acid 
  

   having 
  been 
  converted 
  to 
  the 
  condition 
  of 
  the 
  pentoxide. 
  It 
  

   was 
  found 
  that 
  if 
  dependence 
  is 
  placed 
  upon 
  the 
  occurrence 
  of 
  

   the 
  so-called 
  clear 
  green 
  color 
  of 
  the 
  liquid 
  to 
  determine 
  the 
  

   end 
  of 
  the 
  distillation, 
  it 
  may 
  frequently 
  happen 
  that 
  free 
  

   iodine 
  remains 
  in 
  the 
  residue. 
  This 
  takes 
  place, 
  it 
  will 
  be 
  

   observed, 
  in 
  the 
  atmosphere 
  of 
  carbon 
  dioxide, 
  so 
  that 
  the 
  

   presence 
  of 
  the 
  free 
  iodine 
  can 
  by 
  no 
  possibility 
  be 
  attributed 
  

   to 
  the 
  action 
  of 
  atmospheric 
  air 
  upon 
  the 
  hydriodic 
  acid 
  

   remaining 
  after 
  the 
  distillation 
  is 
  complete. 
  On 
  the 
  other 
  

   hand, 
  it 
  appeared 
  that, 
  if 
  the 
  distillation 
  is 
  pushed 
  too 
  far, 
  the 
  

   molybdenum 
  pentoxide 
  may 
  be 
  still 
  further 
  reduced 
  with 
  con- 
  

   sequent 
  evolution 
  of 
  more 
  than 
  the 
  expected 
  amount 
  of 
  iodine. 
  

   The 
  attainment 
  of 
  an 
  exact 
  degree 
  of 
  reduction 
  with 
  the 
  

   expulsion 
  of 
  the 
  corresponding 
  amount 
  of 
  iodine 
  becomes, 
  

   therefore, 
  a 
  matter 
  of 
  chance 
  unless 
  further 
  precautions 
  are 
  

   taken. 
  We 
  found 
  in 
  our 
  experiments 
  that, 
  if 
  amounts 
  less 
  

   than 
  0'3 
  grm. 
  of 
  the 
  molybdic 
  acid 
  are 
  introduced 
  in 
  soluble 
  

   form 
  into 
  the 
  100 
  cm3 
  retort 
  with 
  a 
  not 
  too 
  great 
  excess 
  of 
  

   potassium 
  iodide, 
  and 
  the 
  40 
  cm3 
  of 
  liquid 
  so 
  constituted 
  that 
  

   2Qcm3 
  £ 
  •£ 
  s 
  j 
  )a 
  jj 
  ^ 
  e 
  wa 
  j- 
  er 
  aric 
  [ 
  20 
  cm3 
  the 
  strongest 
  hydrochloric 
  

   acid, 
  the 
  reduction 
  proceeds 
  with 
  a 
  fair 
  degree 
  of 
  regularity 
  in 
  

   the 
  manner 
  expected. 
  We 
  found 
  it 
  important 
  to 
  restrict 
  the 
  

   excess 
  of 
  potassium 
  iodide 
  so 
  that 
  it 
  shall 
  never 
  exceed 
  the 
  

   theoretical 
  requirement 
  by 
  more 
  than 
  0'5 
  grm. 
  

  

  Our 
  determinations 
  with 
  the 
  pure 
  molybdenum 
  trioxide 
  

   showed 
  errors 
  varying 
  from 
  *0010 
  grm. 
  + 
  to 
  '0007 
  grm. 
  — 
  ; 
  

   the 
  variations 
  from 
  theory 
  in 
  the 
  experiments 
  with 
  ammonium 
  

   molybdate 
  ranged 
  from 
  '0011 
  grm. 
  + 
  to 
  '0011 
  grm. 
  — 
  . 
  If 
  

   these 
  results 
  are 
  compared 
  with 
  those 
  given 
  by 
  Friedheim 
  and 
  

   Euler, 
  the 
  advantage 
  is 
  a 
  little 
  in 
  favor 
  of 
  the 
  latter 
  ; 
  but 
  a 
  

  

  