﻿Dissociation 
  Pressures 
  of 
  Sulphides. 
  

  

  191 
  

  

  C 
  = 
  + 
  1497*56707. 
  A 
  comparison 
  of 
  the 
  values 
  of 
  p 
  com- 
  

   puted 
  from 
  the 
  constants, 
  with 
  the 
  values 
  observed 
  are 
  given 
  

   in 
  Table 
  VIII. 
  

  

  Table 
  VII. 
  

  

  Dissociation 
  pressures 
  of 
  pyrite 
  from 
  575° 
  to 
  680°.* 
  

  

  Tempera- 
  

   ture 
  

   of 
  

   sulphide 
  

   inC° 
  

  

  Tempera- 
  

   ture 
  

   limits 
  of 
  

   sulphur 
  

   inC° 
  

  

  Correspond- 
  

   ing 
  

   pressure 
  limits 
  

   of 
  sulphur 
  in 
  

   mm. 
  of 
  mercury 
  

  

  Mean 
  

  

  dissociation 
  

  

  pressure 
  in 
  mm. 
  

  

  of 
  mercury 
  

  

  Estimated 
  

  

  error 
  

  

  in 
  mm. 
  

  

  680 
  

  

  418-421 
  

  

  505-530 
  

  

  518 
  

  

  ±13 
  

  

  672 
  

  

  393-395 
  

  

  337-349 
  

  

  343 
  

  

  ± 
  6 
  

  

  665 
  

  

  378-380 
  

  

  243-259 
  

  

  251 
  

  

  + 
  8 
  

  

  655 
  

  

  363-364 
  

  

  166-170 
  

  

  168 
  

  

  ± 
  2 
  

  

  645 
  

  

  341-342-7 
  

  

  105-108 
  

  

  106-5 
  

  

  + 
  1-5 
  

  

  635 
  

  

  314-316 
  

  

  60-62 
  

  

  61*0 
  

  

  + 
  1-0 
  

  

  625 
  

  

  288-291 
  

  

  35-37*5 
  

  

  36*3 
  

  

  ± 
  1-3 
  

  

  610 
  

  

  250-255 
  

  

  12-15-0 
  

  

  13-5 
  

  

  ± 
  1-5 
  

  

  595 
  

  

  209-228 
  

  

  3-0- 
  4-0 
  

  

  3-5 
  

  

  ± 
  0-5 
  

  

  575 
  

  

  167-183 
  

  

  0-5- 
  1-0 
  

  

  0*75 
  

  

  ± 
  0-25 
  

  

  *The 
  upper 
  pressure 
  limit 
  was 
  the 
  lowest 
  pressure 
  actually 
  found 
  at 
  

   which 
  the 
  product 
  was 
  entirely 
  non-magnetic 
  ; 
  the 
  lower 
  pressure 
  limit 
  was 
  

   the 
  highest 
  actually 
  found 
  at 
  which 
  magnetic 
  substance 
  was 
  detected. 
  

  

  Table 
  VIII. 
  

  

  Comparison 
  of 
  observed 
  and 
  calculated 
  values 
  of 
  p, 
  the 
  

   dissociation 
  pressure 
  of 
  pyrite. 
  

  

  Abs. 
  temp. 
  

  

  Temp. 
  C° 
  

  

  p 
  observed 
  

  

  p 
  cal. 
  

  

  cliff. 
  

  

  953 
  

  

  680 
  

  

  518 
  

  

  447 
  

  

  + 
  71-0 
  

  

  945 
  

  

  672 
  

  

  343 
  

  

  343 
  

  

  o-o 
  . 
  

  

  938 
  

  

  665 
  

  

  251 
  

  

  264 
  

  

  — 
  13-0 
  

  

  928 
  

  

  655 
  

  

  168 
  

  

  173 
  

  

  - 
  5-0 
  

  

  918 
  

  

  645 
  

  

  106-5 
  

  

  106.5 
  

  

  o-o 
  

  

  908 
  

  

  635 
  

  

  61-0 
  

  

  62-0 
  

  

  — 
  1-0 
  

  

  898 
  

  

  625 
  

  

  36-3 
  

  

  33-5 
  

  

  -f- 
  2-8 
  

  

  883 
  

  

  610 
  

  

  13-5 
  

  

  11-7 
  

  

  + 
  1-8 
  

  

  868 
  

  

  595 
  

  

  3-5 
  

  

  3-5 
  

  

  o-o 
  

  

  848 
  

  

  575 
  

  

  0-75 
  

  

  0-5 
  

  

  4- 
  0-25 
  

  

  In 
  a 
  former 
  paper 
  from 
  this 
  laboratoryf 
  it 
  was 
  stated 
  that 
  

   with 
  hydrogen 
  sulphide 
  gas 
  at 
  1 
  atmosphere 
  pressure, 
  pyrite 
  

   and 
  pyrrhotite 
  appeared 
  to 
  be 
  in 
  equilibrium 
  at 
  565°-575°. 
  By 
  

   an 
  extrapolation 
  of 
  the 
  curve 
  of 
  Preunner 
  and 
  Schupp,*]: 
  the 
  par- 
  

  

  f 
  Allen, 
  Crenshaw 
  and 
  Johnston, 
  The 
  mineral 
  sulphides 
  of 
  iron, 
  this 
  Jour- 
  

   nal, 
  xxxiii, 
  pp. 
  203-204, 
  1912. 
  

  

  JZ. 
  phys. 
  Chem., 
  lxviii, 
  161, 
  1909. 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XLIII, 
  No. 
  255.— 
  March, 
  1917. 
  

   14 
  

  

  