﻿62 
  

  

  Mixter 
  — 
  Heat 
  of 
  Formation 
  of 
  the 
  

  

  Pyrite 
  and 
  Marcasite. 
  — 
  Pyrite 
  from 
  Danbury, 
  Conn., 
  was 
  

   found 
  to 
  have 
  very 
  nearly 
  the 
  composition 
  of 
  5FeS 
  2 
  -fFeS. 
  

   Very 
  likely 
  the 
  mineral 
  had 
  lost 
  sulphur 
  as 
  dioxide 
  when 
  

   pulverized. 
  The 
  average 
  of 
  three 
  combustions 
  was 
  3241 
  c 
  and, 
  

   allowing 
  for 
  ferrous 
  sulphide 
  present, 
  3321 
  c 
  for 
  1 
  gram 
  of 
  

   FeS 
  2 
  . 
  At 
  the 
  time 
  this 
  result 
  was 
  not 
  regarded 
  as 
  satisfactory 
  

   because 
  of 
  the 
  composition 
  of 
  the 
  substance 
  used. 
  Hence 
  

   another 
  crystal 
  of 
  pyrite, 
  locality 
  unknown, 
  was 
  analyzed 
  and 
  

   also 
  marcasite 
  from 
  Joplin, 
  Mo., 
  with 
  the 
  following 
  results 
  : 
  

  

  Iron 
  

  

  Sulphur. 
  . 
  

   Insoluble 
  

  

  Pyrite 
  

  

  47*1 
  

  

  52-6 
  

  

  0-1 
  

  

  99-8 
  

  

  Marcasite 
  

  

  47*1 
  

  

  52*5 
  

  

  0-2 
  

  

  99'8 
  

  

  Theory, 
  FeS 
  5 
  

   46*54$ 
  

   53'46^ 
  

  

  100-00 
  

  

  The 
  results 
  of 
  the 
  combustions 
  were 
  as 
  follows 
  

  

  Pyrite 
  

  

  Marcasite. 
  

  

  FeS, 
  - 
  

  

  Sodium 
  peroxide 
  24* 
  

  

  Water 
  equiv. 
  of 
  system 
  

   Temperature 
  interval. 
  . 
  

  

  4-011 
  

  

  4-059 
  

  

  4-030 
  

  

  4-070 
  

  

  w 
  

  

  24- 
  

  

  27- 
  

  

  27- 
  

  

  4045 
  

  

  4085 
  

  

  4147 
  

  

  4180 
  

  

  3-301 
  

  

  3-316 
  

  

  3-233 
  

  

  3-251° 
  

  

  13352 
  

  

  13545 
  

  

  13407 
  

  

  13589° 
  

  

  — 
  40 
  

  

  — 
  50 
  

  

  — 
  40 
  

  

  — 
  40 
  

  

  13312 
  

  

  13496 
  

  

  13367 
  

  

  13549 
  

  

  3318 
  

  

  3325 
  

  

  ' 
  3317 
  

  

  3329 
  

  

  grms. 
  

  

  Heat 
  effect 
  13352 
  

  

  " 
  " 
  of 
  iron 
  

  

  " 
  " 
  FeS 
  2 
  ... 
  

   " 
  " 
  of 
  1 
  grm._ 
  

  

  The 
  results 
  indicate 
  that 
  the 
  heat 
  of 
  formation 
  of 
  the 
  two 
  

   minerals 
  is 
  the 
  same. 
  Allen, 
  Crenshaw 
  and 
  Johnston* 
  find 
  

   that 
  pyrite 
  is 
  more 
  stable 
  than 
  marcasite, 
  and 
  suggest 
  that 
  the 
  

   latter 
  may 
  have 
  a 
  lower 
  heat 
  of 
  formation 
  than 
  the 
  former. 
  

   In 
  their 
  paperf 
  in 
  the 
  Zeitschrift 
  fur 
  Anorganische 
  Chemie, 
  

   they 
  notice 
  that 
  CarazziJ 
  found 
  the 
  heat 
  of 
  combustion 
  of 
  

   pyrite 
  and 
  marcasite 
  to 
  be 
  the 
  same, 
  namely, 
  1550 
  c 
  . 
  If 
  the 
  

   two 
  crystalline 
  forms 
  of 
  iron 
  disulphide 
  differ 
  as 
  suggested 
  the 
  

   difference 
  is 
  small. 
  

  

  The 
  average 
  of 
  the 
  results 
  obtained 
  with 
  sodium 
  peroxide 
  is 
  

   3322 
  c 
  . 
  For 
  the 
  gram 
  molecule 
  it 
  is 
  398,500 
  c 
  . 
  From 
  this 
  num- 
  

   ber 
  the 
  heat 
  of 
  formation 
  of 
  FeS 
  9 
  is 
  derived 
  as 
  follows 
  : 
  

  

  UNa 
  2 
  2 
  96,000 
  c 
  

  

  Fe 
  

  

  2S 
  + 
  6Na 
  a 
  G 
  2 
  (5270 
  X 
  32-07 
  X 
  2) 
  338,000 
  

  

  Fe 
  4- 
  2S 
  + 
  7|Na 
  2 
  2 
  434,000 
  

  

  FeS 
  2 
  + 
  UNa 
  2 
  2 
  398,500 
  

  

  Fe 
  -f 
  2S 
  — 
  FeS 
  2 
  (crys.) 
  35,500 
  

  

  * 
  This 
  Journal, 
  xxxiii, 
  169. 
  f 
  Loc. 
  cit. 
  

  

  {Rend. 
  Accad. 
  Bolona, 
  N. 
  S., 
  ii, 
  205, 
  1898. 
  

  

  