﻿Osmosis 
  and 
  Osmotic 
  Pressure. 
  397 
  

  

  care 
  was 
  taken 
  that 
  water 
  filled 
  the 
  capillary, 
  and 
  the 
  rubber 
  

   tubing 
  on 
  the 
  top 
  of 
  it 
  was 
  filled 
  with 
  distilled 
  water. 
  

  

  Then 
  the 
  vessel 
  A 
  containing 
  the 
  solution 
  is 
  screwed 
  on 
  to 
  

   the 
  disk 
  B. 
  

  

  As 
  to 
  the 
  putting 
  up 
  o£ 
  the 
  cell, 
  I 
  have 
  found 
  it 
  best 
  first 
  

   to 
  put 
  the 
  rubber 
  tubing 
  on 
  the 
  cell 
  and 
  bend 
  the 
  upper 
  end 
  

   of 
  it 
  back 
  on 
  the 
  cell. 
  The 
  fixing 
  of 
  the 
  cell 
  then 
  only 
  takes 
  

   a 
  few 
  seconds, 
  and 
  the 
  whole 
  apparatus 
  can 
  be 
  put 
  up 
  in 
  

   about 
  10 
  minutes. 
  

  

  In 
  the 
  measurements 
  it 
  was 
  necessary 
  to 
  keep 
  a 
  nearly 
  

   constant 
  temperature. 
  This 
  was 
  obtained 
  by 
  putting 
  the 
  

   osmometer 
  into 
  a 
  stone 
  jar, 
  and 
  this 
  again 
  into 
  a 
  larger 
  one. 
  

   The 
  two 
  vessels 
  were 
  either 
  filled 
  with 
  water 
  that 
  had 
  nearly 
  

   the 
  mean 
  temperature 
  of 
  the 
  room 
  or 
  filled 
  with 
  ice- 
  or 
  

   snow-water. 
  

  

  A 
  similar 
  arrangement 
  was 
  used 
  for 
  the 
  manometer, 
  only 
  

   that 
  the 
  vessels 
  were 
  glass 
  cylinders 
  so 
  as 
  to 
  be 
  able 
  to 
  read 
  

   the 
  mercury 
  level 
  without 
  taking 
  the 
  manometer 
  out 
  of 
  the 
  

   thermostat, 
  and 
  here 
  I 
  always 
  let 
  the 
  water 
  take 
  the 
  tempe- 
  

   rature 
  of 
  the 
  room. 
  

  

  Before 
  taking 
  down 
  the 
  apparatus 
  it 
  was 
  well 
  dried. 
  The 
  

   solution 
  was 
  tested 
  in 
  the 
  way 
  described. 
  When 
  the 
  cup 
  A 
  

   is 
  taken 
  down, 
  the 
  rest 
  of 
  the 
  osmometer 
  is 
  washed 
  out 
  with 
  

   water 
  and 
  everything 
  except 
  the 
  membrane 
  itself 
  is 
  dried. 
  

   This 
  is 
  necessary 
  in 
  order 
  to 
  be 
  sure 
  that 
  no 
  sugar 
  should 
  

   come 
  into 
  the 
  cell 
  when 
  it 
  was 
  taken 
  down. 
  The 
  cell 
  is 
  

   emptied 
  by 
  a 
  pipette 
  and 
  the 
  water 
  analysed. 
  

  

  The 
  measurements 
  are 
  made 
  in 
  two 
  different 
  ways. 
  In 
  

   the 
  first 
  method, 
  the 
  capillary 
  that 
  leads 
  to 
  the 
  compressor 
  

   was 
  closed 
  by 
  sealing-wax 
  and 
  the 
  pressure 
  was 
  effected 
  by 
  

   the 
  osmotic 
  action 
  itself. 
  

  

  In 
  the 
  second 
  method, 
  the 
  pressure 
  was 
  raised 
  by 
  means 
  of 
  

   the 
  compressor 
  to 
  the 
  height 
  desired. 
  

  

  Measurements 
  by 
  the 
  First 
  Method. 
  

  

  12. 
  The 
  apparatus 
  being 
  put 
  up 
  was 
  left 
  to 
  itself 
  at 
  

   constant 
  temperature, 
  and 
  the 
  mercury 
  column 
  examined 
  

   until 
  maximum 
  of 
  pressure. 
  Then 
  the 
  rubber 
  tubing 
  on 
  the 
  

   top 
  of 
  the 
  capillary 
  is 
  taken 
  off 
  and 
  the 
  water-level 
  examined 
  

   for 
  some 
  hours. 
  

  

  