﻿398 
  J. 
  H. 
  Pratt 
  — 
  Double 
  Halides 
  of 
  Caesium, 
  

  

  the 
  lower 
  atomic 
  weight 
  are 
  generally 
  more 
  soluble 
  in 
  water, 
  

   form 
  in 
  larger 
  crystals 
  and 
  with 
  more 
  water 
  of 
  crystallization 
  

   than 
  those 
  with 
  higher 
  atomic 
  weight. 
  

  

  Preparation. 
  — 
  The 
  double 
  salts 
  were 
  prepared 
  in 
  each 
  case 
  

   by 
  mixing 
  solutions 
  of 
  the 
  thallic 
  halide 
  with 
  the 
  alkali 
  halide 
  

   in 
  widely 
  varying 
  proportions, 
  evaporating 
  and 
  cooling 
  to 
  crys- 
  

   tallization. 
  With 
  the 
  bromides 
  and 
  iodides 
  the 
  conditions 
  for 
  

   obtaining 
  the 
  double 
  salts 
  were 
  improved 
  by 
  the 
  presence 
  of 
  a 
  

   little 
  free 
  bromine 
  and 
  iodine. 
  

  

  The 
  crystals, 
  soon 
  after 
  forming, 
  were 
  removed 
  from 
  the 
  

   solutions, 
  quickly 
  pressed 
  between 
  filter 
  papers 
  to 
  remove 
  

   the 
  mother-liquor, 
  and, 
  with 
  the 
  exception 
  of 
  the 
  sodium 
  and 
  

   lithium 
  salts, 
  allowed 
  to 
  stand 
  exposed 
  to 
  the 
  air 
  for 
  some 
  time. 
  

   The 
  latter 
  on 
  account 
  of 
  their 
  instability, 
  were 
  placed 
  in 
  

   tightly 
  stoppered 
  weighing-tubes 
  as 
  soon 
  as 
  they 
  were 
  free 
  

   from 
  the 
  mother-liquor. 
  

  

  Method 
  of 
  analysis. 
  — 
  In 
  determining 
  thallium, 
  the 
  salt 
  was 
  

   dissolved 
  in 
  warm 
  water 
  and 
  a 
  slight 
  excess 
  of 
  ammonium 
  

   sulphide 
  added 
  to 
  precipitate 
  the 
  thallium 
  as 
  thallous 
  sulphide. 
  

   This 
  was 
  filtered 
  and 
  washed 
  with 
  water 
  containing 
  a 
  little 
  

   ammonium 
  sulphide. 
  The 
  precipitate 
  was 
  then 
  dissolved 
  in 
  

   hot 
  dilute 
  nitric 
  acid, 
  the 
  solution 
  evaporated 
  with 
  sulphuric 
  

   acid 
  in 
  a 
  platinum 
  crucible, 
  and 
  then 
  heated 
  to 
  constant 
  weight 
  

   within 
  a 
  porcelain 
  crucible 
  over 
  a 
  small 
  flame. 
  The 
  filtrate 
  

   from 
  the 
  thallous 
  sulphide 
  precipitation, 
  was 
  evaporated 
  with 
  

   sulphuric 
  acid, 
  the 
  ammonium 
  salts 
  driven 
  off, 
  and 
  the 
  residual 
  

   alkali 
  sulphate 
  ignited 
  in 
  a 
  stream 
  of 
  air 
  containing 
  ammonia. 
  

   The 
  halogens 
  were 
  determined 
  as 
  silver 
  salts 
  in 
  separate 
  por- 
  

   tions, 
  with 
  the 
  precaution 
  of 
  adding 
  sulphurous 
  acid 
  in 
  the 
  

   case 
  of 
  the 
  iodides 
  to 
  prevent 
  loss 
  of 
  iodine 
  in 
  dissolving, 
  and 
  

   it 
  was 
  found 
  to 
  be 
  necessary 
  in 
  all 
  cases 
  to 
  use 
  a 
  large 
  excess 
  

   of 
  nitric 
  acid 
  in 
  order 
  to 
  obtain 
  the 
  silver 
  halide 
  in 
  a 
  pure 
  con- 
  

   dition. 
  Water 
  was 
  determined 
  by 
  igniting 
  in 
  a 
  combustion 
  

   tube, 
  behind 
  a 
  layer 
  of 
  dry 
  sodium 
  carbonate, 
  in 
  a 
  stream 
  of 
  

   dry 
  air 
  and 
  collecting 
  it 
  in 
  a 
  weighed 
  calcium 
  chloride 
  tube. 
  

  

  3:1 
  Cmsium 
  and 
  Rubidium 
  Thallic 
  Chlorides, 
  Cs 
  3 
  TlC/ 
  6 
  . 
  

   Hf) 
  and 
  Bb 
  2 
  TWl 
  6 
  . 
  H^O. 
  — 
  The 
  csesium 
  salt 
  is 
  obtained, 
  as 
  a 
  

   white 
  precipitate, 
  when 
  0*25 
  g. 
  of 
  thallic 
  chloride 
  is 
  added 
  to 
  

   a 
  solution 
  of 
  50 
  g. 
  of 
  csesium 
  chloride. 
  The 
  precipitate 
  dis- 
  

   solves 
  somewhat 
  slowly 
  upon 
  heating 
  the 
  solution 
  and 
  crystal- 
  

   lizes 
  out 
  on 
  cooling. 
  The 
  range 
  of 
  conditions 
  is 
  very 
  narrow 
  

   as 
  3 
  g. 
  of 
  thallic 
  chloride 
  to 
  50 
  g. 
  of 
  caesium 
  chloride 
  give 
  the 
  

   salt, 
  Cs 
  2 
  TlCl 
  5 
  . 
  The 
  salt 
  is 
  soluble 
  in 
  hot 
  water, 
  but 
  Cs 
  3 
  Tl 
  2 
  01 
  9 
  

   crystallizes 
  from 
  the 
  solution. 
  

  

  The 
  rubidium 
  salt 
  has 
  a 
  much 
  wider 
  range 
  of 
  formation. 
  It 
  

   is 
  obtained 
  when 
  1*5 
  to 
  25 
  g. 
  of 
  thallic 
  chloride 
  are 
  added 
  to 
  a 
  

   solution 
  of 
  40 
  g. 
  of 
  rubidium 
  chloride. 
  It 
  is 
  very 
  soluble 
  in 
  

  

  