﻿Mack 
  and 
  Hulett 
  — 
  Water 
  Content 
  of 
  Coal. 
  91 
  

  

  these 
  various 
  methods 
  here, 
  as 
  they 
  have 
  been 
  treated 
  at 
  length 
  

   in 
  the 
  literature.* 
  

  

  We 
  will, 
  however, 
  consider 
  at 
  this 
  place 
  the 
  method 
  by 
  

   which 
  coal 
  is 
  dried 
  in 
  a 
  vacuum 
  over 
  such 
  dehydrating 
  agents 
  

   as 
  concentrated 
  sulphuric 
  acid 
  or 
  phosphorus 
  pentoxide. 
  This 
  

   method 
  has 
  been 
  regarded 
  as 
  most 
  reliable, 
  since 
  there 
  is 
  no 
  

   oxygen 
  in 
  contact 
  with 
  the 
  coal 
  and 
  also 
  since 
  it 
  gives 
  higher 
  

   results 
  than 
  most 
  other 
  analytical 
  methods. 
  But 
  it 
  does 
  not 
  

   follow 
  that 
  it 
  really 
  gives 
  the 
  true 
  water 
  content 
  of 
  coal, 
  for 
  it 
  

   is 
  based 
  on 
  the 
  assumption 
  that 
  by 
  dehydrating 
  coal 
  in 
  a 
  

   vacuum 
  at 
  room 
  temperatnre 
  all 
  of 
  the 
  water 
  may 
  be 
  removed 
  

   by 
  these 
  reagents 
  in 
  experimental 
  time. 
  This, 
  however, 
  

   involves 
  a 
  fundamental 
  point 
  in 
  this 
  problem 
  ; 
  as 
  a 
  matter 
  of 
  

   fact, 
  we 
  have 
  found 
  that 
  dehydration 
  at 
  room 
  temperature 
  

   still 
  leaves 
  with 
  the 
  coal 
  a 
  considerable 
  portion 
  of 
  its 
  water 
  

   content. 
  The 
  following 
  experiments, 
  in 
  which 
  we 
  used 
  widely 
  

   different 
  kinds 
  of 
  coal, 
  were 
  made 
  to 
  test 
  this 
  point. 
  

  

  The 
  samples 
  were 
  powdered 
  (20-30 
  mesh), 
  weighed 
  out 
  in 
  

   crucibles 
  and 
  permitted 
  to 
  stand 
  in 
  large 
  vacuum 
  desiccators 
  

   (2-3 
  mm 
  pressure) 
  over 
  fresh 
  phosphorus 
  pentoxide 
  for" 
  7-14 
  

   days 
  or 
  until 
  repeated 
  weighings 
  from 
  day 
  to 
  day 
  showed 
  con- 
  

   stant 
  weight 
  to 
  ±0*2 
  milligram. 
  The 
  desiccator 
  was 
  provided 
  

   with 
  a 
  small 
  electric 
  heater 
  into 
  which 
  the 
  coal 
  crucible 
  just 
  

   fitted 
  so 
  that 
  the 
  coal 
  could 
  be 
  heated 
  inside 
  the 
  desiccator 
  

   when 
  desired. 
  A 
  very 
  short 
  thermometer 
  (from 
  a 
  set) 
  was 
  

   adjusted 
  so 
  that 
  the 
  bulb 
  was 
  imbedded 
  in 
  the 
  coal. 
  After 
  the 
  

   coal 
  had 
  been 
  desiccated 
  until 
  it 
  showed 
  no 
  further 
  loss, 
  it 
  was 
  

   warmed 
  up 
  gradually 
  and 
  maintained 
  finally 
  at 
  a 
  definite 
  tem- 
  

   perature 
  for 
  a 
  few 
  minutes. 
  In 
  every 
  case 
  there 
  was 
  a 
  marked 
  

   loss 
  of 
  water 
  from 
  the 
  coal 
  which 
  had 
  apparently 
  attained 
  equi- 
  

   librium 
  with 
  the 
  first 
  hydrate 
  of 
  phosphorus 
  pentoxide 
  at 
  

   ordinary 
  temperature. 
  The 
  accompanying 
  table 
  gives 
  the 
  

   results. 
  

  

  None 
  of 
  the 
  above 
  losses 
  resulting 
  from 
  the 
  application 
  of 
  

   heat 
  was 
  due 
  to 
  the 
  evolution 
  of 
  gases 
  (other 
  than 
  water) 
  

   since 
  the 
  amount 
  of 
  these 
  was 
  determined 
  and 
  corrections 
  

   made. 
  This 
  was 
  done 
  as 
  follows 
  : 
  Previous 
  to 
  heating, 
  each 
  

   of 
  the 
  samples 
  had 
  been 
  run 
  in 
  duplicate, 
  one 
  crucible 
  with 
  its 
  

   contents 
  being 
  placed 
  in 
  the 
  electric 
  heater 
  just 
  described, 
  

   the 
  other 
  being 
  heated 
  to 
  the 
  same 
  temperature 
  (or 
  10°-30° 
  

   higher) 
  in 
  an 
  apparatus 
  where 
  the 
  gas 
  was 
  collected 
  and 
  its 
  

   volume 
  and 
  weight 
  measured. 
  The 
  weight 
  of 
  the 
  gas 
  evolved 
  

   in 
  each 
  case 
  was 
  subtracted 
  from 
  the 
  total 
  loss 
  on 
  heating 
  and 
  

   the 
  amount 
  of 
  water 
  lost 
  by 
  each 
  of 
  the 
  six 
  samples 
  was 
  thus 
  

   obtained. 
  The 
  corrections 
  were 
  small, 
  lying 
  between 
  the 
  

  

  * 
  For 
  example, 
  see 
  Huntly 
  and 
  Coste, 
  The 
  Determination 
  of 
  Moisture, 
  

   Jour. 
  Soc. 
  Chem. 
  Ind., 
  xxxii, 
  p. 
  62. 
  

  

  