﻿Dissociation 
  Pressures 
  of 
  Sulphides. 
  1 
  95 
  

  

  cases 
  where 
  mercury 
  gauges 
  can 
  not 
  be 
  used. 
  It 
  is 
  intended 
  

   especially 
  for 
  sulphides. 
  It 
  depends 
  in 
  principle 
  upon 
  balanc- 
  

   ing 
  the 
  dissociation 
  pressure 
  of 
  the 
  sulphide 
  by 
  the 
  vapor 
  pres- 
  

   sure 
  of 
  sulphur 
  at 
  a 
  known 
  temperature 
  ; 
  the 
  pressure 
  is 
  not 
  

   directly 
  measured. 
  The 
  method 
  applies 
  to 
  other 
  compounds 
  

   than 
  sulphides 
  provided 
  there 
  is 
  a 
  single 
  volatile 
  dissociation 
  

   product 
  which 
  does 
  not 
  attack 
  glass 
  (or 
  quartz 
  glass) 
  and 
  which 
  

   condenses 
  at 
  accessible 
  temperatures, 
  The 
  method 
  can 
  not 
  be 
  

   used 
  above 
  about 
  1100° 
  to 
  1200°. 
  

  

  2. 
  By 
  this 
  method 
  the 
  dissociation 
  pressure 
  curves 
  of 
  covel- 
  

   lite 
  (CuS) 
  and 
  pyrite 
  (FeS 
  2 
  ) 
  have 
  been 
  determined 
  from 
  about 
  

   l 
  mm 
  to 
  500 
  mm 
  . 
  

  

  3. 
  The 
  chief 
  advantage 
  of 
  the 
  method 
  is 
  that 
  the 
  equilibrium 
  

   is 
  approached 
  from 
  both 
  directions 
  and 
  the 
  experimenter 
  is 
  

   therefore 
  not 
  liable 
  to 
  be 
  deceived 
  by 
  false 
  equilibria. 
  The 
  

   method 
  has 
  the 
  disadvantage 
  of 
  being 
  slow 
  and 
  is 
  inaccurate 
  

   at 
  pressures 
  much 
  above 
  an 
  atmosphere. 
  

  

  4. 
  The 
  method 
  was 
  devised 
  as 
  an 
  instrument 
  for 
  the 
  inves- 
  

   tigation 
  of 
  complex 
  sulphide 
  systems 
  where 
  the 
  dissociation 
  

   pressure 
  is 
  a 
  factor 
  in 
  stability 
  that 
  can 
  not 
  be 
  neglected. 
  

   There 
  seems 
  to 
  be 
  no 
  reason 
  why 
  it 
  should 
  not 
  find 
  a 
  broader 
  

   application 
  to 
  other 
  systems 
  of 
  similar 
  characteristics. 
  

  

  5. 
  The 
  method 
  also 
  supplies 
  a 
  convenient 
  means 
  for 
  the 
  

   synthesis 
  of 
  sulphides 
  the 
  dissociation 
  of 
  which 
  causes 
  difficulty. 
  

  

  Geophysical 
  Laboratory, 
  

  

  Carnegie 
  Institution 
  of 
  Washington, 
  

   Washington, 
  D. 
  C, 
  November 
  22, 
  1916. 
  

  

  