﻿J. 
  J. 
  Stevenson 
  — 
  Origin 
  of 
  Formkohle. 
  215 
  

  

  several 
  others, 
  the 
  passage 
  from 
  one 
  type 
  of 
  coal 
  to 
  the 
  other 
  

   coincides 
  with 
  decreasing 
  thickness 
  of 
  cover. 
  Raefler 
  main- 
  

   tains 
  that 
  the 
  relation 
  between 
  character 
  and 
  mass 
  of 
  cover, 
  on 
  

   one 
  side, 
  and 
  the 
  character 
  of 
  the 
  coal, 
  on 
  the 
  other, 
  is 
  so 
  in- 
  

   timate, 
  that 
  study 
  of 
  maps 
  recently 
  published 
  by 
  the 
  Prussian 
  

   Landesanstalt 
  should 
  enable 
  one 
  to 
  determine 
  beforehand 
  the 
  

   kind 
  of 
  coal 
  likely 
  to 
  be 
  found 
  at 
  any 
  given 
  locality. 
  He 
  finds 
  

   no 
  evidence 
  to 
  support 
  the 
  suggestion 
  that 
  the 
  Formkohle 
  of 
  

   Sachsen 
  is 
  other 
  than 
  autochthonous. 
  

  

  Raefler 
  recognizes 
  that 
  the 
  geographical 
  distribution 
  of 
  lip- 
  

   tobiolithic* 
  materials 
  is 
  an 
  important 
  element 
  in 
  the 
  discus- 
  

   sion. 
  As 
  the 
  records 
  of 
  only 
  three 
  concerns 
  making 
  Montan- 
  

   wachs 
  were 
  available, 
  he 
  gathered 
  material 
  for 
  direct 
  study 
  

   from 
  110 
  localities, 
  representing 
  all 
  parts 
  of 
  the 
  region. 
  The 
  

   liptobiolith 
  content 
  was 
  ascertained 
  in 
  part 
  by 
  extraction 
  of 
  

   the 
  bitumens 
  and 
  in 
  part 
  by 
  determination 
  of 
  the 
  tar-yield. 
  

   He 
  does 
  not 
  regard 
  distillation 
  as 
  the 
  proper 
  method 
  of 
  deter- 
  

   mining 
  the 
  quantity 
  of 
  "bitumen," 
  though 
  that 
  was 
  chosen 
  by 
  

   Potonie 
  and 
  other 
  students. 
  Tar 
  and 
  "bitumen" 
  are 
  not 
  

   equivalent 
  terms 
  ; 
  filter 
  paper 
  yields 
  tar 
  by 
  dry 
  distillation, 
  

   but 
  it 
  is 
  not 
  a 
  bituminous 
  substance. 
  He 
  prefers 
  Graefe's 
  

   definition, 
  that" 
  bitumen" 
  is 
  the 
  material 
  extracted 
  by 
  an 
  

   organic 
  solvent, 
  such 
  as 
  benzol. 
  

  

  One 
  must 
  agree 
  with 
  Raefler 
  in 
  accepting 
  this 
  definition, 
  

   for 
  it 
  distinguishes 
  sharply 
  between 
  substances 
  actually 
  exist- 
  

   ing 
  in 
  the 
  coal 
  and 
  those 
  produced 
  by 
  decomposition 
  during 
  

   destructive 
  distillation. 
  The 
  necessity 
  for 
  this 
  distinction 
  was 
  

   emphasized 
  long 
  ago 
  by 
  Mulder 
  and 
  by 
  Angus 
  Smith 
  in 
  their 
  

   study 
  of 
  peats. 
  f 
  Balfour, 
  many 
  years 
  ago, 
  showed 
  that 
  the 
  

   products 
  of 
  distillation 
  depend 
  very 
  largely 
  upon 
  varying 
  con- 
  

   ditions 
  during 
  the 
  process 
  ; 
  and 
  the 
  matter 
  has 
  been 
  made 
  

   abundantly 
  clear 
  in 
  recent 
  years 
  by 
  the 
  studies 
  of 
  Porter 
  and 
  

   Ovitz,^; 
  who 
  analyzed 
  gases 
  obtained 
  at 
  different 
  temperatures. 
  

   Their 
  experiments 
  confirm 
  the 
  conclusions 
  reached 
  by 
  Emer- 
  

   son 
  McMillin 
  and 
  Henry 
  L. 
  Doherty, 
  who 
  have 
  tested 
  all 
  types 
  

   of 
  coal 
  in 
  their 
  great 
  gas 
  plants 
  in 
  many 
  cities 
  of 
  the 
  United 
  

   States. 
  They 
  assert 
  that 
  reported 
  results 
  of 
  investigation 
  are 
  

   not 
  comparable, 
  unless 
  all 
  conditions 
  under 
  which 
  the 
  work 
  

   was 
  conducted 
  are 
  known. 
  Raefler 
  states 
  that 
  coal, 
  from 
  

   which 
  the 
  " 
  bitumen 
  " 
  has 
  been 
  removed 
  by 
  benzol, 
  yields 
  

  

  * 
  A 
  term 
  introduced 
  by 
  Potonie 
  to 
  designate 
  " 
  Harz-, 
  Wachsharz- 
  and 
  

   Wachs-bildungen, 
  die 
  bei 
  ihrer 
  schwerer 
  Zersetlichkeit 
  nach 
  der 
  Verwesung 
  

   von 
  Pflanzenteilen, 
  die 
  diese 
  Produkte 
  entkalten, 
  zuruckbleiben. 
  7 
  ' 
  (" 
  Entste- 
  

   hung," 
  p. 
  3.) 
  

  

  f-See 
  "Interrelations 
  of 
  the 
  Fossil 
  Fuels, 
  I,'' 
  Proc. 
  Anier. 
  Phil. 
  Soc, 
  vol. 
  

   lv, 
  1916, 
  pp. 
  103, 
  104. 
  

  

  %YL. 
  C. 
  Porter 
  and 
  F. 
  K. 
  Ovitz, 
  " 
  The 
  Volatile 
  Matter 
  of 
  Coal," 
  Bureau 
  of 
  

   Mines, 
  Bull. 
  I, 
  p. 
  26. 
  

  

  