﻿Coefficient 
  of 
  Diffusion. 
  877 
  

  

  seems 
  probable 
  that 
  the 
  disadvantage 
  of 
  using 
  such 
  a 
  delicate 
  

   suspension 
  as 
  a 
  fibre 
  of 
  unspun 
  silk 
  may 
  be 
  overcome 
  by 
  

   using 
  a 
  tine 
  wire 
  in 
  its 
  place, 
  provided 
  that 
  the 
  surface 
  of 
  

   the 
  liquid 
  be 
  covered 
  with 
  a 
  film 
  of 
  oil. 
  When 
  it 
  is 
  re- 
  

   membered 
  that 
  the 
  fibre 
  supports 
  the 
  flask 
  inside 
  a 
  metal 
  

   vessel 
  surrounded 
  by 
  ice, 
  and 
  that 
  clamping 
  and 
  stirring- 
  

   must 
  be 
  carried 
  on 
  without 
  the 
  experimenter 
  being 
  able 
  to 
  

   see 
  what 
  is 
  happening 
  inside 
  the 
  vessel, 
  the 
  advantage 
  of 
  using 
  

   a 
  somewhat 
  stronger 
  suspension 
  will 
  be 
  apparent. 
  

  

  In 
  the 
  present 
  experiments, 
  however, 
  the 
  cocoon 
  suspen- 
  

   sion 
  was 
  adhered 
  to, 
  and 
  with 
  this 
  no 
  oil-film 
  should 
  be 
  used. 
  

  

  In 
  order 
  to 
  find 
  what 
  value 
  must 
  be 
  taken 
  for 
  8 
  in 
  the 
  

   various 
  diffusion 
  experiments, 
  the 
  method 
  of 
  successive 
  ap- 
  

   proximations 
  was 
  used. 
  The 
  final 
  rate 
  of 
  increase 
  in 
  weight 
  

   is 
  first 
  assumed 
  to 
  be 
  due 
  entirely 
  to 
  the 
  salt 
  which 
  enters 
  

   the 
  apparatus. 
  In 
  this 
  way 
  a 
  rough 
  value 
  of 
  the 
  concen- 
  

   tration 
  inside 
  the 
  apparatus 
  at 
  the 
  end 
  of, 
  say, 
  a 
  fortnight, 
  is 
  

   deduced. 
  This 
  gives 
  us 
  a 
  rough 
  value 
  for 
  8, 
  by 
  means 
  of 
  

   which 
  our 
  first 
  assumption 
  may 
  be 
  corrected, 
  and 
  so 
  yield 
  a 
  

   more 
  exact 
  value 
  of 
  8. 
  

  

  9. 
  The 
  Length 
  of 
  the 
  Tube. 
  

  

  Some 
  experiments 
  were 
  also 
  carried 
  out 
  with 
  tabes 
  of 
  

   various 
  lengths. 
  It 
  has 
  already 
  been 
  shown 
  that 
  it 
  is 
  likely 
  

   that 
  to 
  our 
  present 
  degree 
  of 
  accuracy 
  no 
  end 
  correction 
  is 
  

   requisite 
  to 
  the 
  tube 
  of 
  4 
  cms. 
  length. 
  It 
  may 
  be 
  pointed 
  

   out 
  that 
  the 
  end 
  correction 
  must 
  depend 
  on 
  both 
  the 
  length 
  

   and 
  the 
  diameter 
  of 
  the 
  tube. 
  The 
  longer 
  the 
  tube 
  the 
  less 
  

   is 
  the 
  rate 
  of 
  diffusion 
  through 
  it, 
  and 
  therefore 
  the 
  more 
  

   perfectly 
  can 
  gravity 
  regulate 
  uniformity 
  of 
  density 
  in 
  a 
  

   given 
  horizontal 
  plane. 
  

  

  Three 
  tubes 
  were 
  employed, 
  the 
  lengths 
  being 
  4 
  cms., 
  

   2 
  cms., 
  and 
  1 
  cm. 
  ; 
  the 
  areas 
  of 
  cross-section 
  being 
  respec- 
  

   tively 
  1'697, 
  1*025, 
  and 
  1*059 
  sq. 
  cms., 
  and 
  the 
  diameters 
  

   being 
  1*465, 
  1*14, 
  and 
  1*16 
  cms. 
  respectively 
  ; 
  and 
  the 
  solution 
  

   employed 
  was 
  a 
  5 
  per 
  cent, 
  solution 
  of 
  KOI. 
  The 
  results 
  

   are 
  plotted 
  on 
  the 
  accompanying 
  graph 
  (PI. 
  XXV. 
  fig. 
  6). 
  

  

  Assuming 
  no 
  appreciable 
  end 
  correction 
  to. 
  the 
  tube 
  of 
  

   4 
  cms. 
  length, 
  it 
  is 
  found 
  that 
  to 
  give 
  the 
  same 
  value 
  for 
  the 
  

   Coefficient 
  of 
  Diffusion 
  in 
  each 
  case, 
  0*036 
  cm. 
  should 
  be 
  added 
  

   to 
  each 
  end 
  of 
  the 
  2 
  cm. 
  tube 
  (i. 
  e. 
  *032 
  of 
  the 
  diameter), 
  and 
  

   0"045 
  cm. 
  to 
  each 
  end 
  of 
  the 
  1 
  cm. 
  tube 
  {i. 
  e. 
  *039 
  of 
  the 
  

   diameter). 
  The 
  results 
  prove 
  conclusively 
  that 
  it 
  will 
  not 
  

   be 
  possible 
  to 
  accelerate 
  the 
  work 
  by 
  using 
  tubes 
  much 
  

   shorter 
  than 
  4 
  cms., 
  unless 
  perhaps 
  a 
  battery 
  of 
  short 
  and 
  

   narrow 
  tubes 
  can 
  be 
  employed. 
  

  

  