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  XCIX. 
  The 
  Mechanism 
  of 
  the 
  Adsorption 
  (" 
  Sorption 
  ") 
  of 
  

   Hydrogen 
  hy 
  Carbon. 
  By 
  James 
  W. 
  McBain, 
  M,A,, 
  Ph.D,^ 
  

  

  ADSORPTION 
  is 
  quite 
  variously 
  regarded 
  by 
  different 
  

   authorities 
  as 
  one 
  of 
  the 
  following 
  : 
  — 
  

  

  a. 
  True 
  chemical 
  combination. 
  

  

  h. 
  True 
  solid 
  solution. 
  

  

  6*. 
  A 
  modified 
  solid 
  solution 
  in 
  which 
  practically 
  only 
  

  

  the 
  outer 
  layers 
  become 
  saturated 
  owing 
  to 
  the 
  

  

  difficulty 
  of 
  diffusion 
  in 
  solids. 
  

   d. 
  Condensation 
  on 
  the 
  outside 
  of 
  the 
  surface 
  of 
  the 
  

  

  solid. 
  

  

  The 
  first 
  two 
  hypotheses, 
  chemical 
  combination 
  or 
  simple 
  

   -solid 
  solution, 
  are 
  notoriously 
  at 
  variance 
  with 
  the 
  require- 
  

   ments 
  of 
  thermodynamic 
  theory. 
  The 
  third 
  may 
  be 
  shown 
  

   hy 
  mathematical 
  analysis 
  to 
  be 
  irreconcilable 
  with 
  the 
  known 
  

   laws 
  of 
  diffusion, 
  as 
  I 
  expect 
  to 
  discuss 
  in 
  detail 
  elsewhere, 
  

   and 
  it 
  has 
  further 
  been 
  directly 
  refuted 
  by 
  my 
  measurements 
  

   below. 
  

  

  The 
  fourth 
  hypothesis 
  is 
  found 
  insufficient 
  to 
  explain 
  the 
  

   somewhat 
  complex 
  time 
  relationships 
  studied 
  here, 
  which, 
  

   however, 
  point 
  strikingly 
  to 
  the 
  conclusion 
  that 
  both 
  true 
  

   solid 
  solution 
  (true 
  diffusion) 
  and 
  surface-condensation 
  occur 
  t 
  

   They 
  are 
  independent 
  of 
  each 
  other, 
  and 
  their 
  relative 
  im- 
  

   portance 
  and 
  magnitude 
  depend 
  upon 
  the 
  conditions 
  of 
  the 
  

   experiment. 
  

  

  The 
  non-committal 
  name 
  " 
  sorption 
  " 
  may 
  be 
  coined 
  to 
  

   designate 
  the 
  sum 
  of 
  the 
  phenomena, 
  while 
  '''absorption 
  " 
  and 
  

   '^ 
  adsorption' 
  ' 
  should 
  be 
  restricted 
  to 
  proven 
  cases 
  of 
  the 
  

   solution 
  and 
  surface 
  condensation 
  respectively. 
  

  

  Experimental, 
  

  

  The 
  experiments 
  now 
  to 
  be 
  described 
  differ 
  from 
  all 
  

   previous 
  work 
  in 
  this 
  subject 
  in 
  that 
  the 
  time 
  factor 
  has 
  been 
  

   taken 
  into 
  account 
  and 
  carefully 
  studied. 
  It 
  has 
  been 
  found 
  

   that 
  surface-condensation 
  or 
  ac?sorption 
  of 
  hydrogen 
  by 
  carbon 
  

   requires 
  only 
  a 
  few 
  minutes 
  to 
  attain 
  equilibrium, 
  even 
  at 
  

   the 
  temperature 
  of 
  liquid 
  air. 
  On 
  the 
  other 
  hand 
  diffusion 
  

   into 
  the 
  interior 
  of 
  carbon 
  (absorption, 
  solid 
  solution) 
  requires 
  

   many 
  hours 
  for 
  its 
  completion. 
  

  

  * 
  Communicated 
  by 
  the 
  Author. 
  

  

  t 
  Iodine 
  "adsorbed" 
  from 
  solution 
  by 
  carbon 
  behaves 
  similarly, 
  as 
  

   was 
  shown 
  in 
  this 
  laboratory 
  by 
  0. 
  C. 
  M. 
  Davis, 
  Trans. 
  Chem. 
  Soc. 
  

   (1907) 
  xci. 
  p. 
  1666. 
  His 
  communication 
  was 
  written 
  with 
  a 
  knowledge 
  

   of 
  many 
  of 
  the 
  results 
  of 
  the 
  present 
  paper. 
  

  

  