﻿100 
  Mack 
  and 
  Hidett 
  — 
  Water 
  Content 
  of 
  Coal. 
  

  

  the 
  rate 
  of 
  loss 
  of 
  water 
  is 
  dependent 
  on 
  the 
  thickness 
  of 
  the 
  

   film 
  and 
  surface 
  available 
  we 
  find 
  the 
  loss 
  most 
  pronounced 
  in 
  

   the 
  lignites,"* 
  where 
  ordinary 
  moisture 
  determinations 
  are 
  quite 
  

   useless 
  unless 
  the 
  sample 
  has 
  been 
  properly 
  collected 
  and 
  

   handled. 
  As 
  we 
  approach 
  the 
  anthracite 
  end 
  of 
  the 
  coal 
  series 
  

   the 
  adsorption 
  surface 
  and 
  moisture 
  content 
  are 
  small 
  and 
  vapor 
  

   pressure 
  such 
  that 
  there 
  is 
  relatively 
  little 
  loss 
  or 
  gain 
  under 
  

   ordinary 
  conditions. 
  

  

  In 
  removing 
  water 
  from 
  coal 
  by 
  the 
  use 
  of 
  such 
  drying 
  

   agents 
  as 
  sulphuric 
  acid 
  or 
  phosphorus 
  pentoxide, 
  time 
  is 
  

   gained 
  by 
  reducing 
  the 
  coal 
  to 
  a 
  fine 
  state 
  of 
  division, 
  and 
  by 
  

   using 
  a 
  vacuum. 
  The 
  rate 
  of 
  loss 
  is 
  a 
  maximum 
  at 
  first, 
  fall- 
  

   ing 
  off 
  rapidly 
  as 
  the 
  adsorbed 
  water 
  film 
  becomes 
  thinner 
  and 
  

   finally 
  ceasing 
  when 
  the 
  adsorbed 
  film 
  has 
  been 
  reduced 
  to 
  a 
  

   vapor 
  pressure 
  about 
  equal 
  to 
  that 
  of 
  the 
  dehydrating 
  agent. 
  

   With 
  our 
  best 
  dehydrating 
  agents 
  such 
  as 
  H 
  2 
  S0 
  4 
  and 
  P 
  2 
  5 
  it 
  

   would 
  seem 
  to 
  be 
  impossible 
  to 
  remove 
  the 
  films 
  of 
  water 
  

   which 
  are 
  only 
  a 
  few 
  molecules 
  in 
  thickness. 
  Lewesf 
  con- 
  

   siders 
  that 
  a 
  certain 
  sub-bituminous 
  coal 
  which 
  loses 
  15 
  per 
  

   cent 
  of 
  moisture 
  at 
  105° 
  is 
  composed 
  of 
  humus 
  35 
  per 
  cent, 
  

   hydrocarbons 
  and 
  resinous 
  matter 
  30 
  per 
  cent, 
  carbon 
  residue 
  

   20 
  per 
  cent, 
  — 
  or 
  over 
  50 
  per 
  cent 
  of 
  this 
  coal 
  might 
  be 
  con- 
  

   sidered 
  as 
  colloidal 
  and 
  according 
  to 
  the 
  approximate 
  calcula- 
  

   tion 
  previously 
  made 
  the 
  adsorption 
  surface 
  is 
  sufficient 
  to 
  

   retain 
  some 
  3 
  per 
  cent 
  of 
  water 
  in 
  a 
  layer 
  one 
  or 
  two 
  mole- 
  

   cules 
  thick, 
  so 
  that 
  it 
  would 
  not 
  be 
  removed 
  by 
  vacuum 
  desic- 
  

   cation 
  with 
  our 
  best 
  dehydrating 
  agents. 
  Many 
  assumptions 
  

   were 
  necessary 
  in 
  making 
  the 
  calculations 
  but 
  they 
  should 
  give 
  

   an 
  idea 
  of 
  the 
  order 
  of 
  magnitude 
  and 
  in 
  fact 
  they 
  agree 
  satis- 
  

   factorily 
  with 
  our 
  experimental 
  results 
  in 
  Table 
  I. 
  

  

  It 
  was 
  to 
  be 
  expected 
  from 
  the 
  first 
  that 
  a 
  rise 
  of 
  tempera- 
  

   ture 
  would 
  increase 
  the 
  vapor 
  pressure 
  of 
  the 
  adsorbed 
  film, 
  

   thus 
  yielding 
  more 
  water. 
  For 
  it 
  is 
  well 
  known 
  that 
  the 
  con- 
  

   densation 
  of 
  water 
  on 
  fine 
  materials 
  is 
  accompanied 
  by 
  an 
  

   evolution 
  of 
  heat, 
  i. 
  e., 
  the 
  process 
  by 
  which 
  water 
  in 
  mass 
  

   passes 
  into 
  a 
  film 
  having 
  a 
  greater 
  density, 
  is 
  exothermic. 
  

   Consequently, 
  according 
  to 
  the 
  law 
  of 
  Le 
  Chatelier, 
  the 
  appli- 
  

   cation 
  of 
  heat 
  to 
  such 
  a 
  film 
  as 
  that 
  on 
  the 
  colloidal 
  humus 
  

   must 
  result 
  in 
  diminishing 
  the 
  density 
  and 
  the 
  surface 
  tension 
  

   of 
  the 
  film, 
  with 
  a 
  corresponding 
  increase 
  in 
  the 
  vapor 
  pres- 
  

   sure. 
  In 
  fact 
  it 
  has 
  been 
  shown 
  that 
  the 
  density 
  of 
  film 
  water 
  

   approaches 
  that 
  of 
  water 
  in 
  " 
  bulk 
  " 
  as 
  the 
  temperature 
  of 
  both 
  

   is 
  raised 
  the 
  same 
  amount, 
  and 
  of 
  course 
  at 
  the 
  critical 
  tem- 
  

   perature 
  365° 
  the 
  density 
  of 
  both 
  become 
  equal 
  to 
  that 
  of 
  

   water 
  vapor. 
  

  

  * 
  G. 
  H. 
  Frankforter, 
  Jour. 
  Amer. 
  Chem. 
  Soc., 
  xxix, 
  p. 
  1488. 
  

   f 
  Lewes, 
  The 
  Carbonisation 
  of 
  Coal, 
  p. 
  48. 
  

  

  