﻿Dissociation 
  Pressures 
  of 
  Sulphides. 
  

  

  185 
  

  

  phide 
  has 
  gained 
  or 
  lost 
  sulphur 
  or 
  has 
  remained 
  unchanged. 
  

   This 
  may 
  always 
  be 
  determined 
  by 
  an 
  analysis 
  of 
  the 
  product 
  

   and 
  perhaps, 
  with 
  sufficient 
  care 
  in 
  handling, 
  it 
  might 
  be 
  deter- 
  

   mined 
  by 
  weighing 
  the 
  sulphide 
  before 
  and 
  after 
  the 
  experi- 
  

   ment, 
  though 
  this 
  latter 
  method 
  so 
  far 
  has 
  not 
  been 
  tried. 
  In 
  

   special 
  cases 
  the 
  question 
  may 
  be 
  settled 
  by 
  the 
  change 
  in 
  some 
  

   physical 
  property. 
  Thus 
  the 
  dissociation 
  of 
  covellite 
  is 
  most 
  

   readily 
  detected 
  by 
  an 
  inspection 
  of 
  the 
  color. 
  Covellite 
  is 
  

   deep 
  blue, 
  while 
  chalcocite, 
  its 
  dissociation 
  product, 
  is 
  dark 
  

   grey. 
  Small 
  lumps 
  of 
  the 
  mineral 
  about 
  2 
  mm 
  in 
  diameter 
  were 
  

   found 
  very 
  convenient 
  to 
  handle 
  and 
  on 
  such 
  surfaces 
  as 
  they 
  

   presented 
  the 
  colors 
  could 
  be 
  easily 
  distinguished. 
  Such 
  lumps 
  

   of 
  covellite 
  are 
  readily 
  penetrated 
  by 
  sulphur 
  vapor 
  under 
  these 
  

   conditions, 
  for 
  in 
  a 
  number 
  of 
  cases 
  the 
  lumps 
  were 
  removed 
  

   from 
  the 
  apparatus 
  after 
  experiment, 
  broken 
  open 
  and 
  exam- 
  

   ined 
  with 
  a 
  lens, 
  and 
  the 
  change 
  was 
  nearly 
  always 
  complete. 
  

   A 
  pure 
  synthetic 
  covellite 
  was 
  used 
  in 
  some 
  of 
  the 
  experi- 
  

   ments 
  ; 
  in 
  others 
  chalcocite 
  either 
  natural 
  or 
  synthetic. 
  The 
  

   natural 
  chalcocite, 
  from 
  Butte, 
  Montana,* 
  showed 
  the 
  follow- 
  

   ing 
  composition 
  : 
  

  

  Cal. 
  for 
  Cu 
  a 
  S 
  

  

  Cu 
  79-67 
  79-85 
  k 
  

  

  S 
  20*16 
  20-15 
  

  

  Fe 
  _ 
  -14 
  

  

  SiO„ 
  -09 
  

  

  100-06 
  

  

  100-00 
  

  

  Frequently 
  lumps 
  of 
  both 
  chalcocite 
  and 
  covellite 
  were 
  used 
  in 
  

   the 
  same 
  experiment 
  but 
  the 
  resulting 
  products 
  could 
  never 
  be 
  

   distinguished 
  from 
  one 
  another 
  except 
  by 
  the 
  shape 
  of 
  the 
  

   lumps. 
  The 
  results 
  follow 
  : 
  

  

  Table 
  II. 
  

   Dissociation 
  pressures 
  of 
  covellite 
  from 
  400° 
  to 
  490° 
  

  

  Temperature 
  

   of 
  sulphide 
  

  

  Temperature 
  

   limits 
  of 
  sul- 
  

  

  Corresponding 
  pres- 
  

   sure 
  limits 
  of 
  the 
  

   sulphur 
  in 
  mm. 
  of 
  

  

  Mean 
  dissoci- 
  

   ation 
  pressure 
  

   in 
  mm. 
  of 
  

  

  Estimated 
  

   error 
  in 
  

  

  inC° 
  

  

  phur 
  in 
  C° 
  

  

  mercury 
  

  

  mercury 
  

  

  mm. 
  

  

  400- 
  

  

  183 
  

  

  -198 
  

  

  1- 
  2 
  

  

  1-5 
  

  

  =fc 
  I' 
  

  

  410- 
  

  

  198 
  ■ 
  

  

  -210 
  

  

  2- 
  3-4 
  

  

  2-7 
  

  

  zfc 
  0-7 
  

  

  433-7 
  

  

  246 
  

  

  -251 
  

  

  10-1 
  2 
  -.5 
  

  

  11-2 
  

  

  =b 
  1' 
  

  

  450- 
  

  

  280 
  ■ 
  

  

  -284 
  

  

  30-32 
  

  

  31-0 
  

  

  zfc 
  1- 
  

  

  460- 
  

  

  306 
  ■ 
  

  

  -315 
  

  

  50-60 
  

  

  55-0 
  

  

  zfc 
  5" 
  

  

  468- 
  

  

  334 
  • 
  

  

  -337 
  

  

  90-96 
  

  

  93- 
  

  

  zfc 
  3- 
  

  

  475- 
  

  

  363 
  

  

  -365 
  

  

  166- 
  174 
  

  

  170- 
  

  

  zfc 
  4- 
  

  

  482- 
  

  

  389 
  

  

  -391 
  

  

  314-326 
  

  

  320- 
  

  

  zfc 
  6- 
  

  

  485- 
  

  

  401 
  

  

  -403 
  

  

  386- 
  399 
  

  

  393- 
  

  

  zfc 
  7- 
  

  

  490- 
  

  

  417-5 
  

  

  -420 
  

  

  501-520 
  

  

  510- 
  

  

  ±: 
  10- 
  

  

  * 
  Analyzed 
  by 
  Eugen 
  Posnjak. 
  

  

  