﻿Dissociation 
  Pressures 
  of 
  Sulphides. 
  189 
  

  

  heavy 
  metals 
  were 
  found. 
  Both 
  sulphur 
  and 
  iron 
  were 
  deter- 
  

   mined. 
  

  

  Found 
  Cal. 
  

  

  Fe 
  = 
  46-71 
  46-56 
  

  

  S 
  = 
  53-29 
  53-44 
  

  

  SiO„ 
  = 
  trace 
  ? 
  

   Heavy 
  metals 
  

   of 
  H 
  2 
  S 
  group 
  = 
  trace 
  ? 
  

  

  100-00 
  100-00 
  

  

  Pyrite 
  does 
  not 
  seem 
  so 
  readily 
  penetrated 
  by 
  sulphur 
  vapor 
  

   as 
  covellite 
  even 
  at 
  a 
  much 
  higher 
  temperature. 
  Covellite 
  has 
  

   a 
  perfect 
  cleavage, 
  and 
  lumps 
  of 
  it 
  are 
  always 
  filled 
  with 
  seams 
  

   while 
  pyrite 
  shows 
  a 
  smooth 
  conchoidal 
  fracture. 
  For 
  this 
  

   reason, 
  probably, 
  pyrite 
  dissociates 
  much 
  more 
  slowly 
  than 
  

   covellite. 
  Even 
  after 
  four 
  or 
  five 
  hours 
  heating 
  the 
  100 
  mesh 
  

   pyrite 
  powder 
  used 
  in 
  the 
  experiments 
  was 
  only 
  partially 
  

   changed. 
  The 
  dissociated 
  portion, 
  i. 
  e. 
  the 
  pyrrhotite, 
  

   amounted 
  to 
  about 
  one-third 
  to 
  one-half 
  of 
  the 
  original 
  pyrite. 
  

   It 
  was 
  of 
  a 
  somewhat 
  darker 
  tint 
  and 
  crystallized 
  in 
  mossy 
  

   aggregations. 
  

  

  The 
  magnetic 
  test 
  for 
  pyrrhotite. 
  — 
  The 
  difference 
  in 
  mag- 
  

   netic 
  susceptibility 
  between 
  pyrite 
  and 
  pyrrhotite 
  affords 
  a 
  

   fairly 
  sensitive 
  method 
  for 
  separating 
  them. 
  An 
  ordinary 
  

   horseshoe 
  magnet 
  however 
  is 
  unsuitable. 
  We 
  employed 
  a 
  

   strong 
  electro-magnet 
  for 
  the 
  purpose. 
  

  

  The 
  glass 
  apparatus 
  containing 
  the 
  sulphide 
  need 
  not 
  be 
  

   opened 
  for 
  the 
  preliminary 
  magnetic 
  test. 
  After 
  cooling, 
  the 
  

   bulb, 
  C 
  (fig. 
  1), 
  is 
  brought 
  close 
  to 
  the 
  poles 
  of 
  the 
  magnet. 
  

   Unless 
  the 
  quantity 
  of 
  pyrrhotite 
  is 
  small, 
  some 
  particles 
  will 
  

   show 
  attraction 
  very 
  plainly. 
  If 
  the 
  test 
  is 
  negative, 
  it 
  is 
  

   necessary 
  to 
  open 
  the 
  bulb, 
  remove 
  and 
  triturate 
  the 
  sulphide 
  

   in 
  an 
  agate 
  mortar 
  and 
  test 
  it 
  again. 
  The 
  magnet 
  will 
  now 
  

   in 
  some 
  cases 
  remove 
  a 
  little 
  pyrrhotite. 
  As 
  a 
  control 
  on 
  the 
  

   results 
  obtained 
  with 
  the 
  magnet, 
  a 
  number 
  of 
  the 
  products 
  

   were 
  also 
  analyzed. 
  The 
  analyses 
  were 
  all 
  carefull} 
  7 
  done 
  in 
  a 
  

   platinum 
  dish, 
  the 
  iron 
  being 
  twice 
  precipitated 
  with 
  ammonium 
  

   hydroxide 
  which 
  was 
  prepared 
  by 
  saturating, 
  with 
  ammonia 
  

   gas, 
  water 
  contained 
  in 
  a 
  gold 
  vessel. 
  The 
  following 
  table 
  

   shows 
  the 
  agreement 
  between 
  the 
  magnetic 
  tests 
  and 
  the 
  

   analyses. 
  

  

  The 
  percentage 
  of 
  iron 
  in 
  pure 
  pyrite 
  is 
  46*56. 
  All 
  the 
  

   magnetic 
  products 
  contained 
  more 
  iron 
  than 
  this. 
  (See 
  Table 
  

   VI.) 
  The 
  non-magnetic 
  products 
  which 
  were 
  analyzed 
  gave 
  

   4:6-90, 
  4:6-73, 
  4:6*99, 
  47*39. 
  The 
  first 
  three 
  results 
  are 
  as 
  close 
  

   to 
  pyrite 
  as 
  could 
  be 
  expected. 
  The 
  last 
  is 
  the 
  only 
  real 
  dis- 
  

  

  