﻿Osmosis 
  and 
  Osmotic 
  Pressure. 
  409 
  

  

  The 
  Velocity 
  Curves. 
  

  

  16. 
  The 
  dependence 
  of 
  the 
  velocities 
  A/ 
  upon 
  the 
  pressure 
  

   7r 
  is 
  graphically 
  represented 
  by 
  a 
  series 
  of 
  curves, 
  figs. 
  9, 
  10, 
  

   11, 
  12, 
  13, 
  11 
  (PI. 
  IX.). 
  

  

  We 
  see 
  that 
  in 
  all 
  cases 
  the 
  observed 
  velocities 
  determine 
  

   a 
  well-defined 
  curve. 
  

  

  In 
  figs. 
  9, 
  10, 
  13, 
  and 
  14 
  it 
  is 
  only 
  velocities 
  near 
  to 
  the 
  

   reversion 
  point 
  that 
  are 
  measured. 
  

  

  Figs. 
  11 
  and 
  12, 
  however, 
  corresponding 
  to 
  the 
  expe- 
  

   riments 
  I., 
  II., 
  III., 
  give 
  the 
  curves 
  from 
  7r 
  = 
  to 
  a 
  pressure 
  

   far 
  beyond 
  the 
  equilibrium 
  pressure, 
  and 
  we 
  shall 
  first 
  consider 
  

   these 
  more 
  complete 
  curves. 
  

  

  17. 
  Curve 
  corresponding 
  to 
  experiment 
  I. 
  (fig. 
  11, 
  curve 
  I.). 
  

  

  — 
  When 
  we 
  start 
  from 
  the 
  point 
  it 
  = 
  the 
  velocities 
  

  

  dX' 
  

   diminish 
  rapidlv 
  and 
  -=— 
  decreases, 
  then 
  we 
  have 
  an 
  

  

  dX 
  f 
  C7r 
  

  

  inflexion 
  point 
  -= 
  — 
  having 
  a 
  minimum 
  value. 
  The 
  inflexion 
  

  

  point 
  lies 
  in 
  this 
  case 
  very 
  near 
  to 
  the 
  reversion 
  point. 
  

  

  dX' 
  

   After 
  passing 
  these 
  points 
  the 
  quantity 
  -=— 
  begins 
  to 
  increase 
  

  

  and 
  continues 
  to 
  do 
  so 
  until 
  we 
  reach 
  a 
  certain 
  point 
  cor- 
  

   responding 
  to 
  the 
  pressure 
  7r=83"9 
  atm. 
  and 
  a 
  velocity 
  

   X' 
  = 
  130 
  mm./hour. 
  ^ 
  

  

  Here 
  we 
  have 
  a 
  sudden 
  fall 
  in 
  the 
  value 
  of 
  - 
  n 
  — 
  . 
  The 
  

  

  air 
  

  

  turning 
  of 
  the 
  curve 
  is 
  so 
  sharply 
  defined, 
  that 
  we 
  must 
  

  

  dX 
  f 
  

   regard 
  it 
  as 
  a 
  point 
  of 
  discontinuity 
  in 
  the 
  function 
  -h— 
  . 
  Before 
  

  

  this 
  point 
  , 
  — 
  has 
  the 
  value 
  19*5 
  expressed 
  in 
  our 
  units'; 
  on 
  

  

  the 
  other 
  side 
  of 
  the 
  point 
  - 
  — 
  is 
  nearly 
  equal 
  to 
  zero. 
  This 
  

  

  point 
  we 
  shall 
  call 
  the 
  characteristic 
  point 
  of 
  the 
  velocity 
  

   curve. 
  From 
  this 
  point 
  the 
  curve 
  goes 
  nearly 
  horizontal, 
  

   the 
  velocities 
  being 
  nearly 
  constant. 
  

  

  The 
  measured 
  velocities 
  even 
  show 
  some 
  decrease 
  ; 
  but 
  

   this 
  is 
  not 
  greater 
  than 
  can 
  be 
  ascribed 
  to 
  faults 
  in 
  the 
  

   observations. 
  First 
  at 
  a 
  pressure 
  of 
  about 
  95 
  atm. 
  we 
  shall 
  

   notice 
  a 
  remarkable 
  increase 
  of 
  the 
  velocity, 
  and 
  by 
  increasing 
  

   pressure 
  the 
  curve 
  bends 
  upwards. 
  

  

  18. 
  Curves 
  corresponding 
  to 
  a 
  concentration 
  320 
  gr./l. 
  

  

  Experiment 
  II. 
  represented 
  by 
  fig. 
  11, 
  curves 
  II. 
  & 
  III. 
  

   III. 
  „ 
  fig. 
  12. 
  

  

  The 
  temperature 
  is 
  about 
  the 
  same 
  for 
  all 
  four 
  curves. 
  

   The 
  two 
  curves 
  fig. 
  11 
  (II.) 
  and 
  fig. 
  12 
  (I.) 
  correspond 
  to 
  

  

  