﻿98 
  Mack 
  and 
  Hidett 
  — 
  Water 
  Content 
  of 
  Coal. 
  

  

  1'26X 
  10" 
  8 
  cm. 
  If 
  these 
  latter 
  values 
  are 
  to 
  be 
  regarded 
  as 
  

   probably 
  nearer 
  the 
  truth, 
  then 
  the 
  film 
  cannot 
  be 
  more 
  than 
  a 
  

   few 
  molecules 
  thick. 
  The 
  density 
  of 
  the 
  film 
  has 
  been 
  put 
  

   (for 
  25° 
  C.) 
  at 
  about 
  twice 
  that 
  of 
  water, 
  namely 
  at 
  2. 
  ' 
  It 
  is 
  

   to 
  be 
  noted, 
  however, 
  that 
  the 
  first 
  few 
  layers 
  of 
  molecules 
  

   next 
  to 
  the 
  colloidal 
  surface 
  represent 
  a 
  greater 
  density 
  than 
  

   the 
  layers 
  more 
  removed, 
  which 
  in 
  fact 
  probably 
  grade 
  off 
  

   imperceptibly 
  into 
  the 
  bulk 
  water, 
  making 
  it 
  hard 
  to 
  say 
  just 
  

   exactly 
  where 
  the 
  " 
  film' 
  1 
  really 
  begins. 
  

  

  If 
  we 
  consider 
  one 
  cubic 
  centimeter 
  of 
  the 
  organic 
  sub- 
  

   stances 
  which 
  make 
  up 
  coal, 
  free 
  from 
  water 
  and 
  ash, 
  it 
  would 
  

   have 
  a 
  density 
  of 
  not 
  much 
  over 
  1. 
  If 
  the 
  cube 
  were 
  divided 
  

   into 
  little 
  cubes 
  10' 
  6 
  cm. 
  on 
  each 
  edge 
  — 
  a 
  particle 
  readily 
  

   detected 
  by 
  the 
  ultra-microscope 
  — 
  the 
  area 
  of 
  the 
  faces 
  of 
  these 
  

   little 
  cubes 
  would 
  be 
  600 
  square 
  meters. 
  If 
  we 
  suppose 
  that 
  

   they 
  are 
  covered 
  with 
  a 
  layer 
  of 
  water 
  molecules 
  say 
  1X10~ 
  8 
  

   cm. 
  thick 
  with 
  a 
  density 
  of 
  1, 
  although 
  it 
  is 
  probably 
  greater 
  

   than 
  that, 
  there 
  would 
  be 
  *06 
  cc 
  of 
  water 
  on 
  these 
  faces 
  in 
  a 
  con- 
  

   densed 
  condition 
  such 
  that 
  it 
  would 
  show 
  little 
  or 
  no 
  vapor 
  

   pressure. 
  If 
  the 
  layer 
  of 
  water 
  were 
  1/10 
  of 
  the 
  thickness 
  of 
  

   the 
  cube 
  or 
  10 
  molecules 
  thick 
  with 
  the 
  increased 
  size 
  of 
  the 
  

   cubes, 
  there 
  would 
  be 
  about 
  *T 
  CC 
  or 
  60 
  per 
  cent 
  water 
  intimately 
  

   associated 
  with 
  this 
  original 
  cubic 
  centimeter 
  of 
  coal 
  substance 
  

   and 
  the 
  vapor 
  pressure 
  of 
  this 
  water 
  would 
  undoubtedly 
  be 
  

   much 
  below 
  that 
  of 
  a 
  plane 
  surface 
  of 
  water 
  at 
  the 
  same 
  tem- 
  

   perature. 
  The 
  substance 
  would 
  no 
  doubt 
  take 
  up 
  water 
  from 
  

   ordinary 
  air 
  and 
  " 
  feel 
  dry." 
  

  

  Some 
  of 
  the 
  particles 
  of 
  coal 
  are 
  probably 
  as 
  small 
  or 
  smaller 
  

   than 
  we 
  have 
  assumed 
  — 
  others 
  larger, 
  the 
  humus 
  material 
  in 
  

   general 
  being 
  in 
  the 
  colloidal 
  condition 
  outlined. 
  In 
  the 
  

   progress 
  of 
  the 
  transformation 
  of 
  peat 
  to 
  bituminous 
  coal, 
  as 
  

   the 
  chemical 
  reactions 
  slowly 
  result 
  in 
  the 
  disappearance 
  of 
  the 
  

   humus, 
  the 
  waxes, 
  resins, 
  etc. 
  forming 
  carbon 
  residue 
  (compo- 
  

   sition 
  of 
  anthracite), 
  carbon 
  dioxide, 
  volatile 
  hydrocarbons, 
  

   water, 
  and 
  the 
  various 
  other 
  products, 
  there 
  results 
  a 
  gradual 
  

   but 
  marked 
  decrease 
  in 
  the 
  water 
  content 
  proportional 
  to 
  the 
  

   decreased 
  colloidal 
  surface. 
  

  

  The 
  true 
  water 
  content 
  of 
  any 
  coal 
  might 
  thus 
  be 
  taken 
  as 
  a 
  

   rough 
  measure 
  of 
  its 
  humus 
  content, 
  and 
  vice 
  versa.* 
  

  

  The 
  condition 
  of 
  water 
  on 
  " 
  adsorption 
  " 
  surfaces 
  was 
  first 
  

   studied 
  by 
  Van 
  Bemmelenf 
  who 
  experimented 
  in 
  particular 
  

   with 
  silicic 
  acid 
  and 
  ferric 
  oxide 
  gels. 
  The 
  method 
  used 
  was 
  

   to 
  place 
  weighed 
  amounts 
  of 
  the 
  gels 
  in 
  desiccators 
  where 
  a 
  

   definite 
  vapor 
  pressure 
  was 
  maintained 
  by 
  sulphuric 
  acid 
  of 
  a 
  

  

  * 
  John 
  Harger, 
  Jour. 
  Soc. 
  Chern. 
  Ind., 
  xxxii, 
  p. 
  460, 
  1913, 
  suggested 
  that 
  

   the 
  humus 
  material 
  contained 
  most 
  of 
  the 
  water 
  found 
  in 
  coal. 
  

   f 
  J. 
  M. 
  Van 
  Bemmelen, 
  Die 
  Adsorption, 
  1910. 
  

  

  