﻿194 
  Allen 
  and 
  Lombard 
  — 
  Determination 
  of 
  

  

  advantage 
  is 
  quite 
  important. 
  The 
  two 
  mineral 
  sulphides 
  

   covellite 
  and 
  pyrite 
  reach 
  their 
  equilibrium 
  pressures 
  very 
  

   slowly 
  under 
  the 
  conditions 
  described 
  in 
  this 
  paper. 
  For 
  

   example, 
  1 
  g. 
  pyrite 
  was 
  crushed 
  to 
  a 
  powder 
  which 
  passed 
  a 
  

   screen 
  of 
  100 
  meshes 
  to 
  the 
  inch. 
  After 
  5-6 
  hours 
  heating 
  at 
  

   a 
  temperature 
  of 
  672° 
  and 
  a 
  pressure 
  of 
  3.20 
  mm 
  of 
  sulphur 
  

   vapor, 
  therefore 
  very 
  close 
  to 
  the 
  dissociation 
  pressure 
  curve, 
  

   about 
  10$ 
  remained 
  unchanged 
  while 
  the 
  rest 
  contained 
  49-6$ 
  

   iron 
  and 
  had 
  therefore 
  lost 
  only 
  3% 
  sulphur. 
  A 
  portion 
  of 
  

   this 
  dissociation 
  product 
  was 
  heated 
  a 
  second 
  time 
  under 
  simi- 
  

   lar 
  conditions. 
  Analysis 
  showed 
  that 
  it 
  now 
  contained 
  57% 
  

   iron. 
  It 
  had 
  therefore 
  lost 
  7 
  '§% 
  more 
  sulphur 
  in 
  the 
  second 
  

   heating. 
  Covellite 
  also 
  was 
  found 
  to 
  move 
  slowly 
  to 
  equili- 
  

   brium, 
  though 
  not 
  so 
  slowly 
  as 
  pyrite. 
  

  

  4. 
  The 
  apparatus 
  required 
  is 
  easy 
  to 
  construct, 
  is 
  not 
  fragile, 
  

   and 
  is 
  inexpensive. 
  

  

  5. 
  The 
  most 
  serious 
  disadvantage 
  of 
  this 
  method 
  is 
  the 
  time 
  

   which 
  it 
  involves 
  \ 
  it 
  being 
  necessary 
  to 
  make 
  a 
  number 
  of 
  

   experiments 
  for 
  the 
  determination 
  of 
  every 
  point 
  on 
  the 
  

   curve. 
  The 
  adjustment 
  of 
  the 
  furnace 
  temperatures 
  is 
  also 
  

   tedious, 
  but 
  it 
  is 
  difficult 
  to 
  see 
  how 
  this 
  could 
  be 
  avoided 
  in 
  

   any 
  method, 
  for 
  uniformity 
  in 
  temperature 
  is 
  a 
  prime 
  neces- 
  

   sity 
  in 
  any 
  solution 
  of 
  the 
  problem. 
  

  

  6. 
  The 
  method 
  is 
  not 
  adapted 
  to 
  the 
  measurement 
  of 
  pres- 
  

   sures 
  of 
  much 
  more 
  than 
  an 
  atmosphere, 
  since 
  the 
  vapor 
  pressure 
  

   curve 
  of 
  sulphur 
  in 
  this 
  region 
  becomes 
  so 
  steep 
  that 
  a 
  small 
  

   error 
  in 
  temperature 
  causes 
  a 
  comparatively 
  large 
  error 
  in 
  the 
  

   pressure. 
  

  

  Other 
  uses 
  of 
  the 
  method. 
  — 
  In 
  principle, 
  of 
  course, 
  this 
  

   method 
  for 
  dissociation 
  pressures 
  need 
  not 
  be 
  confined 
  to 
  the 
  

   sulphides 
  ; 
  any 
  compound 
  which 
  dissociates 
  at 
  accessible 
  tem- 
  

   peratures 
  with 
  the 
  formation 
  of 
  a 
  single 
  volatile 
  product 
  which 
  

   condenses 
  at 
  accessible 
  temperatures 
  could 
  be 
  investigated 
  in 
  

   this 
  way. 
  A 
  further 
  proviso 
  is 
  that 
  glass 
  (or 
  quartz 
  glass) 
  

   should 
  stand 
  the 
  chemical 
  action 
  of 
  the 
  vapor 
  sufficiently 
  well. 
  

   The 
  method 
  also 
  affords 
  a 
  convenient 
  means 
  for 
  the 
  synthesis 
  

   of 
  most* 
  sulphides 
  and 
  can 
  be 
  employed 
  to 
  advantage 
  in 
  cer- 
  

   tain 
  instances 
  where 
  dissociation 
  gives 
  trouble. 
  More 
  import- 
  

   ant 
  than 
  this, 
  the 
  method 
  promises 
  to 
  be 
  a 
  valuable 
  instrument 
  

   in 
  'the 
  investigation 
  of 
  complex 
  sulphides 
  which 
  can 
  not 
  be 
  

   synthesized 
  by 
  simple 
  fusion 
  in 
  an 
  indifferent 
  gas. 
  

  

  Summary. 
  

  

  1. 
  A 
  new 
  method 
  has 
  been 
  devised 
  for 
  the 
  determination 
  of 
  

   dissociation 
  pressures 
  at 
  comparatively 
  high 
  temperatures 
  in 
  

  

  * 
  Some 
  sulphides 
  like 
  marcasite 
  could 
  probably 
  not 
  be 
  made 
  in 
  the 
  dry 
  way. 
  

  

  