﻿262 
  Goocfi 
  and 
  Morley 
  — 
  Deter 
  rain 
  ation 
  of 
  Gold. 
  

  

  

  

  

  

  

  

  

  Volume 
  

  

  

  

  

  

  

  

  

  before 
  the 
  

  

  

  

  

  

  

  

  

  addition 
  of 
  

  

  

  

  

  

  

  

  Gold 
  

  

  the 
  thio- 
  

  

  

  Potassium 
  iodide. 
  

  

  

  

  

  chloride 
  

  

  sulphate. 
  

  

  

  OOlgm. 
  

  

  0-02 
  gm. 
  

  

  0-05 
  gm. 
  

  

  01 
  gm. 
  

  

  0-2 
  gm. 
  

  

  00087 
  gm. 
  cms. 
  

  

  cT 
  

  

  ro-81 
  

  

  0-81 
  

  

  0-8i 
  

  

  0-82 
  

  

  0-84 
  

  

  (( 
  

  

  15 
  

  

  l^i 
  

  

  0-77 
  

  

  0-78 
  

  

  0-80 
  

  

  0-81 
  

  

  0-81 
  

  

  (( 
  

  

  25 
  

  

  t 
  i 
  "a 
  

  

  ^ 
  074 
  

  

  0-72 
  

  

  0-78 
  

  

  0-79 
  

  

  0-80 
  

  

  (( 
  

  

  50 
  

  

  w 
  ?- 
  o 
  

  

  .2 
  S5 
  

  

  1 
  0-61 
  

  

  0-61 
  

  

  0-68 
  

  

  0-76 
  

  

  0-79 
  

  

  u 
  

  

  100 
  

  

  a 
  s 
  

  

  [0-45 
  

  

  0-49 
  

  

  0-60 
  

  

  0-72 
  

  

  0-75 
  

  

  (( 
  

  

  200 
  

  

  It 
  is 
  evident 
  that 
  for 
  the 
  smaller 
  amounts 
  of 
  iodide 
  the 
  lib- 
  

   eration 
  of 
  iodine 
  decreases 
  rapidly 
  with 
  the 
  dilution. 
  The 
  

   larger 
  amounts 
  at 
  the 
  highest 
  concentration 
  show 
  readings 
  

   a 
  trifle 
  above 
  the 
  normal 
  — 
  perhaps 
  because 
  the 
  well-known 
  

   effect 
  of 
  concentrated 
  solutions 
  of 
  a 
  soluble 
  iodide 
  upon 
  tlie 
  

   delicacy 
  of 
  the 
  starch 
  end-color 
  begins 
  to 
  appear. 
  At 
  volumes 
  

   lying 
  between 
  the 
  limit 
  of 
  25"=™^ 
  and 
  50°""' 
  O'l 
  grm. 
  of 
  potas- 
  

   sium 
  iodide 
  is 
  an 
  appropriate 
  amount 
  to 
  use 
  ; 
  at 
  a 
  volume 
  of 
  

   25cm3^ 
  O'Ol 
  grm. 
  to 
  0'05 
  grm. 
  of 
  the 
  iodide 
  will 
  do 
  the 
  work 
  ; 
  

   and 
  at 
  lower 
  dilutions, 
  as 
  will 
  appear 
  in 
  the 
  tabular 
  statements 
  

   to 
  follow, 
  even 
  less 
  of 
  the 
  iodide 
  is 
  effective. 
  

  

  In 
  the 
  series 
  of 
  experiments 
  of 
  which 
  the 
  details 
  are 
  given 
  in 
  

   Table 
  I, 
  use 
  was 
  made 
  of 
  a 
  solution 
  of 
  pure 
  gold 
  chloride 
  con- 
  

   taining 
  0*8710 
  grm. 
  to 
  the 
  liter 
  — 
  as 
  determined 
  by 
  careful 
  

   precipitation 
  in 
  the 
  usual 
  manner 
  by 
  ferrous 
  sulphate, 
  and 
  by 
  

   an 
  alkaline 
  solution 
  of 
  formaldehyde 
  according 
  to 
  the 
  method 
  

   of 
  Yanino.* 
  A 
  nearly 
  centinormal 
  solution 
  of 
  iodine 
  was 
  pre- 
  

   pared 
  by 
  diluting 
  to 
  a 
  liter 
  100^"^^ 
  of 
  nearly 
  decinormal 
  iodine 
  

   in 
  potassium 
  iodide 
  carefully 
  standardized 
  against 
  exactly 
  deci- 
  

   normal 
  arsenious 
  acid. 
  A 
  nearly 
  centinormal 
  solution 
  of 
  

   sodium 
  thiosulphate 
  (containing 
  1-7012 
  grm. 
  of 
  Na^S^Og 
  to 
  the 
  

   liter) 
  was 
  made 
  by 
  diluting 
  to 
  a 
  liter 
  lOO'^™^ 
  of 
  a 
  nearly 
  deci- 
  

   normal 
  solution 
  of 
  that 
  reagent 
  which 
  had 
  been 
  standardized 
  

   carefully 
  against 
  the 
  standard 
  iodine 
  prepared 
  as 
  described. 
  

   The 
  solution 
  of 
  potassium 
  iodide 
  employed 
  contained 
  10 
  grm. 
  

   of 
  that 
  salt 
  in 
  the 
  liter. 
  

  

  In 
  conducting 
  the 
  experiments, 
  a 
  convenient 
  amount 
  of 
  the 
  

   solution 
  of 
  gold 
  chloride 
  was 
  drawn 
  from 
  a 
  burette, 
  potassium 
  

   iodide 
  was 
  introduced 
  in 
  the 
  amounts 
  indicated 
  (always 
  several 
  

   times 
  the 
  theoretical 
  equivalent 
  of 
  the 
  gold, 
  and 
  more 
  than 
  

   enough 
  to 
  dissolve 
  the 
  aurous 
  iodide 
  precipitated 
  at 
  first), 
  a 
  

   sufficiency 
  of 
  clear 
  starch 
  indicator 
  was 
  added, 
  the 
  starch 
  blue 
  

   was 
  bleached 
  by 
  the 
  thiosulpliate, 
  and 
  the 
  iodine 
  was 
  added 
  

   until 
  the 
  liquid 
  assumed 
  a 
  faint 
  rose 
  color. 
  Upon 
  the 
  theory 
  

   that 
  potassium 
  iodide 
  sets 
  free 
  two 
  atoms 
  of 
  iodine 
  for 
  every 
  

  

  *Ber. 
  d. 
  d. 
  chem. 
  Gesellsch., 
  xxxi, 
  J 
  763. 
  

  

  