﻿266 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  11 
  

  

  Two 
  methods 
  for 
  the 
  isolation 
  of 
  a 
  chemical 
  individual 
  were 
  discussed. 
  

   The 
  first 
  of 
  these 
  is 
  the 
  treatment 
  of 
  a 
  solution 
  containing 
  two 
  elements 
  in 
  

   such 
  a 
  way 
  as 
  to 
  obtain 
  a 
  compound 
  of 
  one 
  element 
  with 
  properties 
  char- 
  

   acteristically 
  different 
  from 
  the 
  analogous 
  compound 
  of 
  the 
  other 
  element. 
  

   An 
  example 
  was 
  drawn 
  from 
  the 
  treatment 
  of 
  a 
  solution 
  containing 
  copper 
  and 
  

   silver 
  with 
  hydrochloric 
  acid, 
  forming 
  a 
  very 
  slightly 
  soluble 
  chloride 
  of 
  silver 
  

   and 
  a 
  very 
  soluble 
  chloride 
  of 
  copper, 
  thereby 
  permitting 
  the 
  isolation 
  of 
  

   silver. 
  

  

  The 
  other 
  method 
  is 
  required 
  when 
  the 
  elements 
  are 
  so 
  nearly 
  alike 
  in 
  

   their 
  properties 
  that 
  they 
  react 
  identically 
  with 
  all 
  reagents. 
  This 
  condition 
  

   is 
  exemplified 
  by 
  the 
  group 
  of 
  sixteen 
  elements 
  known 
  as 
  the 
  "rare 
  earths." 
  

   This 
  group 
  forms 
  complete 
  series 
  of 
  isomorphous 
  salts, 
  and 
  separations 
  be- 
  

   tween 
  two 
  (or 
  more) 
  members 
  are 
  usually 
  accomplished 
  by 
  fractional 
  crys- 
  

   tallization. 
  In 
  the 
  platinum 
  group 
  either 
  method 
  may 
  be 
  used, 
  although 
  

   the 
  former 
  is 
  used 
  more 
  frequently 
  because 
  it 
  is 
  more 
  rapid. 
  However, 
  in 
  

   one 
  large 
  platinum 
  refinery, 
  platinum 
  is 
  separated 
  from 
  iridium 
  by 
  the 
  frac- 
  

   tional 
  crystallization 
  of 
  the 
  isomorphous 
  salts 
  Na2PtCl6 
  and 
  Na2lrCl6. 
  

  

  It 
  is 
  also 
  possible 
  by 
  appropriate 
  means 
  to 
  treat 
  solutions 
  of 
  iridium 
  and 
  

   platinum 
  in 
  such 
  a 
  way 
  as 
  to 
  reduce 
  iridium 
  from 
  the 
  tetravalent 
  to 
  the 
  

   trivalent 
  condition, 
  without 
  appreciably 
  affecting 
  the 
  platinum. 
  Iridium 
  

   now 
  behaves 
  as 
  a 
  different 
  chemical 
  individual 
  and 
  its 
  double 
  chloride 
  with 
  

   ammonium 
  chloride 
  is 
  quite 
  soluble 
  and 
  not 
  isomorphous 
  with 
  (NH4)2PtCl6. 
  

  

  Such 
  treatment 
  would 
  then 
  effect 
  a 
  very 
  rapid 
  purification 
  of 
  platinum, 
  

   except 
  for 
  the 
  phenomena 
  of 
  "co-precipitation," 
  which 
  is 
  very 
  marked 
  in 
  

   this 
  whole 
  group 
  of 
  elements. 
  Because 
  of 
  this 
  the 
  precipitate 
  of 
  (NH4)2- 
  

   PtCle 
  is 
  contaminated 
  with 
  iridium, 
  and 
  the 
  preparation 
  of 
  platinum 
  in 
  a 
  

   high 
  degree 
  of 
  purity 
  is 
  made 
  possible 
  only 
  by 
  several 
  re-precipitates 
  of 
  the 
  

   compound 
  named. 
  

  

  In 
  the 
  purification 
  of 
  palladium 
  use 
  is 
  made 
  of 
  the 
  characteristic 
  compound 
  di- 
  

   chlorodiammine-palladium-Pd(NH3)2Cl2. 
  For 
  rhodium 
  two 
  salts 
  are 
  used, 
  

   the 
  first 
  refining 
  being 
  accomplished 
  by 
  the 
  use 
  of 
  the 
  insoluble 
  salt 
  KsRh- 
  

   (N02)6, 
  and 
  the 
  subsequent 
  preparation 
  of 
  chloro-pentamine, 
  rhodium 
  

   chloride 
  (Rh(NH3)5Cl)Cl2. 
  For 
  iridium 
  no 
  similar 
  characteristic 
  compound 
  

   is 
  known 
  and 
  iridium 
  must 
  be 
  purified 
  by 
  the 
  opposite 
  procedure 
  of 
  remov- 
  

   ing 
  other 
  elements 
  from 
  the 
  solution 
  first. 
  

  

  Ruthenium 
  and 
  osmium 
  may 
  be 
  separated 
  from 
  the 
  other 
  platinum 
  ele- 
  

   ments 
  through 
  the 
  volatile 
  tetroxides 
  RUO4 
  and 
  OSO4. 
  

  

  In 
  the 
  case 
  of 
  platinum, 
  palladium 
  and 
  rhodium, 
  it 
  is 
  to 
  be 
  noted 
  that 
  in 
  

   each 
  case 
  a 
  salt 
  is 
  chosen 
  which 
  may 
  be 
  ignited 
  directly 
  to 
  metal, 
  leaving 
  

   no 
  other 
  nonvolatile 
  constituents. 
  

  

  Brief 
  mention 
  was 
  made 
  of 
  the 
  work 
  done 
  on 
  the 
  precautions 
  necessary 
  

   to 
  avoid 
  contamination 
  in 
  the 
  melting 
  of 
  the 
  purified 
  platinum 
  sponge. 
  

  

  C. 
  O. 
  Fairchild: 
  Thermo-electric 
  tests 
  for 
  the 
  purity 
  of 
  some 
  metals 
  (illus- 
  

   trated) 
  . 
  

  

  (Author's 
  abstract.) 
  The 
  thermo-electric 
  test 
  is 
  performed 
  by 
  making 
  a 
  

   thermocouple 
  of 
  two 
  metals 
  and 
  measuring 
  its 
  e. 
  m. 
  f 
  . 
  at 
  a 
  known 
  temperature 
  ; 
  

   for 
  example 
  two 
  pieces 
  of 
  gold 
  from 
  different 
  sources 
  may 
  be 
  compared 
  at 
  

   the 
  melting 
  point 
  of 
  gold. 
  If 
  the 
  thermal 
  e. 
  m. 
  f 
  . 
  is 
  large, 
  one 
  or 
  both 
  of 
  the 
  sam- 
  

   ples 
  are 
  quite 
  impure. 
  If 
  the 
  e. 
  m. 
  f 
  . 
  is 
  small 
  then 
  time 
  is 
  well 
  spent 
  in 
  further 
  

   study 
  of 
  the 
  samples. 
  The 
  test 
  is 
  particularly 
  suited 
  to 
  comparing 
  metals 
  of 
  

   the 
  highest 
  purity, 
  containing 
  only 
  spectroscopic 
  traces 
  of 
  one 
  or 
  a 
  very 
  few 
  

   metals. 
  

  

  