﻿Osmosis 
  and 
  Osmotic 
  Pressure. 
  413 
  

  

  velocity 
  curves 
  corresponding 
  to 
  the 
  same 
  temperature 
  and 
  

   concentration 
  mast 
  be 
  ascribed 
  to 
  a 
  difference 
  in 
  the 
  pro- 
  

   perties 
  of 
  the 
  membrane. 
  But 
  if 
  we 
  have 
  to 
  use 
  different 
  

   cells, 
  the 
  question 
  may 
  arise 
  how 
  to 
  find 
  the 
  change 
  due 
  to 
  

   the 
  membrane. 
  It 
  will 
  in 
  general 
  be 
  difficult 
  to 
  find 
  the 
  

   absolute 
  value 
  of 
  the 
  change 
  of 
  velocity 
  due 
  to 
  the 
  change 
  of 
  

   the 
  membrane 
  ; 
  but 
  still 
  we 
  are 
  able 
  from 
  the 
  form 
  of 
  the 
  

   curves 
  to 
  determine 
  whether 
  such 
  changes 
  have 
  occurred. 
  

  

  Suppose 
  we 
  have 
  at 
  the 
  same 
  temperature 
  and 
  concentration 
  

   measured 
  the 
  velocity 
  curves 
  for 
  cells 
  1 
  and 
  2. 
  Let 
  the 
  

   velocities 
  corresponding 
  to 
  a 
  pressure 
  ir 
  be 
  \ 
  and 
  \ 
  2 
  ; 
  then 
  

   if 
  we 
  had 
  membranes 
  with 
  constant 
  qualities 
  all 
  over 
  the 
  

   surface, 
  and 
  if 
  the 
  two 
  membranes 
  had 
  the 
  same 
  qualities^ 
  

   we 
  should 
  have 
  

  

  — 
  independent 
  of 
  ir. 
  

   \ 
  2 
  

  

  If 
  then 
  the 
  quantity—^ 
  varies 
  with 
  tt, 
  this 
  variation 
  must 
  

  

  A/2 
  

  

  be 
  due 
  to 
  a 
  difference 
  in 
  the 
  properties 
  of 
  the 
  membrane. 
  

   Such 
  a 
  variation 
  of 
  the 
  curves 
  that 
  always 
  will 
  make 
  r^ 
  a 
  

  

  ^2 
  

  

  function 
  of 
  the 
  pressure 
  we 
  shall 
  have 
  ivlien 
  the 
  characteristic 
  

   point 
  corresponds 
  to 
  different 
  pressures. 
  

  

  In 
  the 
  experiments 
  here 
  made 
  the 
  same 
  cell 
  has 
  been 
  used, 
  

   and 
  then 
  we 
  can 
  simply 
  say 
  : 
  — 
  The 
  motion 
  and 
  different 
  

   position 
  of 
  the 
  characteristic 
  point 
  correspond 
  to 
  a 
  variation 
  

   in 
  the 
  properties 
  of 
  the 
  membrane. 
  The 
  absolute 
  distance 
  

   between 
  the 
  characteristic 
  points 
  gives 
  no 
  measure 
  of 
  the 
  

   change. 
  It 
  seems 
  a 
  priori 
  probable 
  that 
  a 
  certain 
  distance 
  

   corresponds 
  to 
  a 
  greater 
  change 
  when 
  the 
  characteristic 
  point 
  

   is 
  near 
  to 
  the 
  reversion 
  point 
  than 
  when 
  it 
  is 
  far 
  off. 
  This 
  is 
  

   also 
  confirmed 
  by 
  experiments. 
  In 
  experiment 
  II. 
  the 
  cha- 
  

   racteristic 
  point 
  is 
  very 
  far 
  from 
  the 
  reversion 
  point, 
  and 
  we 
  

   see 
  that 
  a 
  comparatively 
  great 
  motion 
  of 
  the 
  characteristic 
  

   point 
  has 
  caused 
  a 
  very 
  small 
  variation 
  in 
  the 
  reversion 
  

   point. 
  

  

  In 
  experiment 
  III. 
  the 
  characteristic 
  point 
  is 
  near 
  to 
  the 
  

   reversion 
  point, 
  and 
  now 
  a 
  comparatively 
  small 
  motion 
  calls- 
  

   forth 
  a 
  remarkable 
  change 
  in 
  the 
  reversion 
  point. 
  Also 
  in 
  

   experiment 
  IV., 
  where 
  the 
  change 
  of 
  the 
  reversion 
  point 
  is 
  

   very 
  great, 
  the 
  reversion 
  point 
  is 
  near 
  to 
  the 
  characteristic 
  

   point. 
  

  

  The 
  importance 
  of 
  investigations 
  made 
  after 
  this 
  method 
  

   will 
  be 
  evident 
  from 
  the 
  measurements 
  already 
  given. 
  From 
  

  

  