﻿Organic 
  Liquids 
  in 
  Presence 
  of 
  Dust 
  -free 
  Air. 
  307 
  

  

  when 
  adiabatically 
  expanded, 
  no 
  condensation 
  before 
  the 
  

   expansion 
  1*25, 
  and 
  a 
  dense 
  fog 
  instead 
  of 
  a 
  fine 
  rain 
  at 
  

   that 
  point. 
  The 
  natural 
  conclusion 
  is 
  that 
  the 
  rain-like 
  

   condensation 
  for 
  expansions 
  ranging 
  from 
  1*25 
  to 
  1*38 
  is 
  due 
  

   to 
  condensation 
  round 
  a 
  comparatively 
  small 
  number 
  of 
  

   electrical 
  nuclei 
  either 
  existing 
  in 
  the 
  gas 
  or 
  produced 
  by 
  the 
  

   sudden 
  expansion. 
  Here, 
  then, 
  is 
  a 
  case 
  of 
  the 
  condensation 
  

   of 
  the 
  vapour 
  of 
  a 
  liquid 
  of 
  unique 
  ionizing 
  power 
  round 
  

   electrical 
  nuclei. 
  It 
  becomes 
  a 
  matter 
  of 
  interest 
  to 
  compare 
  

   with 
  water-vapour 
  the 
  vapours 
  of 
  other 
  liquids 
  whose 
  ionizing- 
  

   powers 
  are 
  either 
  much 
  smaller 
  or 
  practically 
  zero, 
  and 
  the 
  

   following 
  experiments 
  were 
  carried 
  out 
  for 
  that 
  purpose. 
  

  

  § 
  2. 
  Apparatus. 
  

  

  The 
  apparatus 
  employed 
  was, 
  so 
  far 
  as 
  concerns 
  the 
  method 
  

   used 
  to 
  obtain 
  adiabatic 
  expansion, 
  essentially 
  the 
  same 
  as 
  the 
  

   apparatus 
  described 
  by 
  Wilson 
  in 
  his 
  later 
  experiments. 
  A 
  

   drawing 
  of 
  it 
  is 
  shown 
  on 
  Plate 
  V. 
  a 
  is 
  a 
  glass 
  tube 
  floating 
  

   on 
  mercury 
  and 
  fitting 
  pretty 
  accurately 
  into 
  the 
  cylinder 
  (6). 
  

   The 
  end 
  (e) 
  of 
  the 
  glass 
  rod 
  (c) 
  is 
  rounded 
  into 
  a 
  knob 
  

   and 
  covered 
  with 
  rubber 
  ; 
  it 
  is 
  pressed, 
  by 
  the 
  elasticity 
  of 
  

   the 
  piece 
  of 
  rubber- 
  tubing 
  (d), 
  firmly 
  against 
  the 
  turned-out 
  

   end 
  of 
  the 
  tube 
  (/), 
  into 
  which 
  the 
  rubber-covered 
  knob 
  

   accurately 
  fits. 
  / 
  connects 
  with 
  the 
  vacuous 
  space 
  (g). 
  

   This 
  was 
  a 
  large 
  strong 
  bottle 
  which 
  could 
  be 
  readily 
  evacuated 
  

   by 
  means 
  of 
  a 
  Fleuss 
  vacuum-pump. 
  On 
  pulling 
  the 
  glass 
  

   rod 
  (c), 
  connexion 
  is 
  made 
  between 
  the 
  interior 
  of 
  a 
  and 
  g 
  y 
  

   the 
  result 
  of 
  which 
  is 
  that 
  the 
  piston-tube 
  (a) 
  is 
  suddenly 
  and 
  

   sharply 
  brought 
  down 
  against 
  the 
  smooth 
  flat 
  rubber 
  stopper 
  

   (/*), 
  and 
  a 
  practically 
  adiabatic 
  expansion 
  produced 
  in 
  the 
  

   cloud-vessel 
  (i), 
  where 
  the 
  formation 
  of 
  the 
  rain 
  or 
  fog 
  is 
  

   observed. 
  The 
  lower 
  end 
  of 
  a 
  must 
  be 
  very 
  carefully 
  

   ground 
  flat 
  so 
  that 
  it 
  fits 
  perfectly 
  tightly 
  against 
  the 
  upper 
  

   surface 
  of 
  the 
  rubber 
  stopper. 
  The 
  liquid 
  to 
  be 
  experimented 
  

   on 
  is 
  introduced 
  into 
  i 
  through 
  k, 
  which 
  can 
  be 
  closed 
  by 
  

   a 
  ground-glass 
  cap 
  rendered 
  secure 
  against 
  entrance 
  of 
  air 
  by 
  

   an 
  external 
  mercury 
  seal. 
  The 
  cloud-vessel 
  is 
  connected 
  by 
  

   capillary 
  tubing 
  with 
  the 
  manometer 
  (Z). 
  The 
  mercury 
  in 
  the 
  

   manometer 
  was 
  always 
  brought 
  before 
  an 
  expansion 
  to 
  a 
  fixed 
  

   mark 
  just 
  below 
  the 
  capillary 
  joint 
  by 
  means 
  of 
  the 
  fine 
  

   adjustment 
  (hinge 
  and 
  screw) 
  n. 
  In 
  this 
  way 
  the 
  dead 
  space 
  

   at 
  m 
  was 
  rendered 
  negligibly 
  small. 
  During 
  the 
  expansion 
  

   the 
  tap 
  (p) 
  was 
  closed, 
  and 
  then, 
  when 
  the 
  expanded 
  air 
  and 
  

   vapour 
  had 
  recovered 
  its 
  thermal 
  and 
  saturation 
  equilibrium, 
  

   p 
  was 
  opened 
  and 
  the 
  mercury 
  brought 
  to 
  the 
  same 
  fixed 
  

   mark. 
  The 
  ratio 
  of 
  the 
  pressures, 
  after 
  allowance 
  has 
  been 
  

  

  X2 
  

  

  