﻿Broioning 
  and 
  Hiitchms 
  — 
  Estimation 
  of 
  Thallium. 
  461 
  

  

  and 
  the 
  contents 
  agitated 
  to 
  bring 
  about 
  a 
  good 
  separation 
  of 
  

   the 
  precipitated 
  chroraate. 
  After 
  the 
  precipitate 
  had 
  com- 
  

   pletely 
  settled 
  out 
  and 
  the 
  solution 
  had 
  become 
  cold 
  the 
  chro- 
  

   mate 
  was 
  filtered 
  upon 
  asbestos, 
  as 
  described 
  above, 
  dried 
  over 
  

   a 
  low 
  flame 
  and 
  weighed 
  to 
  a 
  constant 
  weight. 
  The 
  filtrates 
  

   from 
  several 
  determinations 
  were 
  evaporated 
  to 
  a 
  small 
  volume 
  

   and 
  in 
  one 
  or 
  two 
  cases 
  a 
  residue 
  amounting 
  to 
  a 
  few 
  tenths 
  

   of 
  a 
  milligram 
  was 
  obtained, 
  but 
  no 
  appreciable 
  quantity 
  of 
  

   dissolved 
  chromate 
  was 
  thus 
  recovered. 
  It 
  was 
  found 
  that 
  

   when 
  the 
  precipitation 
  was 
  made 
  in 
  the 
  cold 
  the 
  chromate 
  did 
  

   not 
  flock 
  well, 
  but 
  remained 
  partly 
  in 
  a 
  finely 
  divided 
  condi- 
  

   tion 
  which 
  would 
  run 
  through 
  the 
  felt 
  and 
  require 
  repeated 
  

   filtration. 
  The 
  addition 
  of 
  ammonium 
  nitrate 
  before 
  precipi- 
  

   tation 
  prevented 
  this 
  largely, 
  even 
  in 
  the 
  cold, 
  but 
  the 
  best 
  

   results 
  were 
  obtained 
  by 
  warming 
  the 
  solution 
  before 
  precipi- 
  

   tation 
  and 
  using 
  potassium 
  carbonate 
  rather 
  than 
  ammonium 
  

   hydroxide. 
  The 
  results 
  follow 
  in 
  Table 
  I. 
  

  

  Table 
  I. 
  

  

  TINO3 
  taken. 
  TlsCrOi 
  found. 
  Error. 
  

  

  Calculated 
  as 
  TI2O. 
  Calculated 
  as 
  TI2O. 
  Calculated 
  as 
  TI2O. 
  

  

  grm. 
  grm. 
  grm. 
  

  

  (1) 
  00796 
  O-OVOl 
  0-0005 
  — 
  

  

  (2) 
  0-0792 
  0-0788 
  0-0004 
  — 
  

  

  (3) 
  0-0792 
  0-0786 
  0-0006- 
  

  

  (4) 
  0-1188 
  01177 
  0-0011 
  — 
  

  

  (5) 
  0-1192 
  0-1186 
  0-0006 
  — 
  

  

  (6) 
  0-1185 
  0-1178 
  0-0007 
  — 
  

  

  (7) 
  0-1190 
  0-1185 
  00005 
  — 
  

  

  (8) 
  0-1189 
  0-1183 
  0-0006- 
  

  

  (9) 
  0-1196 
  2000 
  0004 
  + 
  

  

  (10) 
  0-1196 
  0-2005 
  0-0009 
  4- 
  

  

  (11) 
  0-1173 
  0-1173 
  00000 
  

  

  (12) 
  0-1171 
  0-1163 
  0-0008 
  — 
  

  

  An 
  attempt 
  was 
  made 
  to 
  estimate 
  the 
  thallium 
  volumetri- 
  

   cally 
  by 
  determining 
  the 
  amount 
  of 
  chromate 
  in 
  the 
  filtrate 
  

   from 
  the 
  thallous 
  chromate, 
  and 
  by 
  difference 
  (the 
  potassium 
  

   dichromate 
  originally 
  added 
  being 
  known) 
  the 
  amount 
  com- 
  

   bined 
  with 
  the 
  thallium 
  in 
  the 
  precipitate. 
  The 
  method 
  used 
  

   to 
  determine 
  the 
  standard 
  of 
  the 
  dichromate 
  solutions 
  and 
  also 
  

   the 
  chromate 
  remaining 
  in 
  the 
  filtrate 
  was 
  described 
  by 
  one 
  of 
  

   us 
  in 
  a 
  previous 
  paper 
  from 
  this 
  laboratory. 
  "^ 
  According 
  to 
  

   this 
  procedure 
  the 
  filtrate 
  from 
  the 
  thallous 
  chromate 
  contain- 
  

   ing 
  the 
  excess 
  of 
  alkali 
  chromate 
  was 
  acidified 
  with 
  sulphuric 
  

   acid, 
  a 
  definite 
  amount 
  of 
  a 
  solution 
  of 
  arsenious 
  oxide, 
  

   previously 
  standardized, 
  was 
  added 
  and 
  the 
  whole 
  was 
  allowed 
  

  

  * 
  This 
  Journal, 
  vol. 
  i, 
  35, 
  1896. 
  

  

  