﻿Osmosis 
  and 
  Osmotic 
  Pressure. 
  261 
  

  

  function 
  of 
  the 
  potential 
  v, 
  this 
  function 
  can 
  be 
  given 
  the 
  form 
  

  

  <x 
  = 
  « 
  + 
  a±v 
  4- 
  a 
  2 
  v 
  2 
  + 
  . 
  . 
  . 
  

  

  a 
  would 
  then 
  be 
  the 
  conductivity 
  corresponding 
  to 
  v 
  = 
  0. 
  By 
  

   putting 
  the 
  values 
  found 
  into 
  a 
  curve 
  we 
  should 
  get 
  for 
  this 
  

   special 
  case 
  a 
  = 
  4*75 
  • 
  10 
  -6 
  ohm 
  -1 
  . 
  

  

  If 
  an 
  electromotive 
  force 
  were 
  required 
  to 
  make 
  the 
  system 
  

   a 
  conductor, 
  we 
  should 
  get 
  a 
  = 
  0, 
  then 
  a 
  — 
  a 
  will, 
  give 
  the 
  

   conductivity 
  produced 
  by 
  the 
  electromotive 
  force, 
  and 
  we 
  see 
  

   that 
  the 
  conductivity 
  for 
  higher 
  potentials 
  is 
  made 
  up 
  of 
  two 
  

   parts, 
  one 
  part 
  a 
  - 
  « 
  produced 
  by 
  the 
  electromotive 
  force 
  and 
  

   one 
  part 
  a 
  belonging 
  to 
  the 
  system. 
  

  

  In 
  our 
  case 
  a 
  is 
  great 
  in 
  comparison 
  to 
  a 
  — 
  a 
  even 
  for 
  

  

  potentials 
  up 
  to 
  175 
  volts. 
  For 
  v 
  = 
  115 
  volts 
  °=0*1. 
  

  

  From 
  this 
  we 
  can 
  conclude 
  that 
  the 
  large 
  temperature 
  effect 
  

   which 
  is 
  measured 
  by 
  a 
  potential 
  of 
  115 
  volts 
  must 
  be 
  mainly 
  

   due 
  to 
  the 
  effect 
  upon 
  « 
  . 
  

  

  In 
  view 
  of 
  the 
  constitution 
  of 
  the 
  membrane, 
  a 
  natural 
  

   explanation 
  of 
  the 
  potential 
  effect 
  can 
  be 
  got 
  by 
  assuming 
  that 
  

   it 
  is 
  due 
  to 
  an 
  inner 
  motion 
  in 
  the 
  membrane 
  produced 
  by 
  

   the 
  mechanical 
  action 
  of 
  the 
  electric 
  force. 
  This 
  also 
  gives 
  

   an 
  explanation 
  of 
  the 
  fact 
  that 
  the 
  resistance 
  generally 
  will 
  

   decrease 
  when 
  electrolysis 
  is 
  continued 
  after 
  maximum, 
  and 
  

   most 
  rapidly 
  in 
  the 
  weakest 
  membranes. 
  

  

  As 
  the 
  potential 
  effect 
  as 
  well 
  as 
  the 
  temperature 
  effect 
  

   corresponds 
  to 
  a 
  nearly 
  constant 
  membrane, 
  we 
  see 
  that, 
  as 
  far 
  

   as 
  the 
  electric 
  resistance 
  can 
  be 
  considered 
  a 
  criterion 
  of 
  a 
  

   good 
  membrane, 
  the 
  resistances 
  must 
  be 
  compared 
  at 
  the 
  

   same 
  temperature 
  and 
  the 
  same 
  potential. 
  

  

  General 
  Remarks 
  as 
  to 
  tlie 
  Treatment 
  of 
  the 
  Observations. 
  

  

  8. 
  Before 
  going 
  on 
  to 
  describe 
  more 
  minutely 
  the 
  special 
  

   observations, 
  we 
  shall 
  see 
  which 
  quantities 
  are 
  to 
  be 
  measured. 
  

   By 
  the 
  term 
  osmotic 
  pressure 
  we 
  shall 
  understand 
  the 
  

   difference 
  between 
  the 
  hydrostatic 
  pressures 
  on 
  the 
  two 
  

   sides 
  of 
  a 
  perfect 
  semipermeable 
  membrane 
  when 
  the 
  solution 
  

   and 
  solvent 
  are 
  in 
  thermodynamic 
  equilibrium. 
  As 
  this 
  

   pressure 
  is 
  a 
  limiting 
  value 
  lor 
  the 
  pressures 
  measurable 
  by 
  

   our 
  membranes, 
  we 
  shall 
  in 
  the 
  following 
  call 
  it 
  the 
  ideal 
  

   equilibrium 
  pressure 
  (ttq) 
  and 
  we 
  have 
  : 
  

  

  ir 
  =p-p 
  =<l)(C,T,j) 
  ) 
  (la) 
  

  

  The 
  problem 
  to 
  be 
  solved 
  is 
  to 
  determine 
  by 
  experiment 
  

   the 
  function 
  cp. 
  C 
  denotes 
  the 
  concentration 
  defined 
  in 
  one 
  

  

  