﻿and 
  other 
  Properties 
  of 
  Thin 
  Oily 
  Films. 
  161 
  

  

  actually 
  in 
  contact. 
  And 
  as 
  regards 
  seizing, 
  there 
  is 
  

   difficulty 
  in 
  understanding 
  why, 
  when 
  it 
  actually 
  occurs, 
  

   rupture 
  should 
  ensue 
  at 
  another 
  place 
  rather 
  than 
  at 
  the 
  

   recently 
  engaged 
  surfaces. 
  

  

  It 
  may 
  perhaps 
  be 
  doubted 
  whether 
  the 
  time 
  is 
  yet 
  ripe 
  

   for 
  a 
  full 
  discussion 
  of 
  the 
  behaviour 
  of 
  the 
  thinnest 
  films, 
  

   bat 
  I 
  will 
  take 
  this 
  opportunity 
  to 
  put 
  forward 
  a 
  few 
  remarks. 
  

   Two 
  recent 
  French 
  writers, 
  Devaux 
  * 
  and 
  Marcelin 
  f, 
  who 
  

   have 
  made 
  interesting 
  contributions 
  to 
  the 
  subject, 
  accept 
  my 
  

   suggestion 
  that 
  the 
  drop 
  of 
  tension 
  in 
  contaminated 
  surfaces 
  

   commences 
  when 
  the 
  iayer 
  is 
  one 
  molecule 
  thick 
  ; 
  but 
  

   Hardy 
  % 
  points 
  out 
  a 
  difficulty 
  in 
  the 
  case 
  of 
  pure 
  oleic 
  acid, 
  

   where 
  it 
  appears 
  that 
  the 
  drop 
  commences 
  at 
  a 
  thickness 
  of 
  

   1*3 
  x 
  10" 
  6 
  mm., 
  while 
  the 
  thickness 
  of 
  a 
  molecule 
  should 
  be 
  

   decidedly 
  less. 
  Many 
  of 
  Devaux' 
  observations 
  relate 
  to 
  the 
  

   case 
  where 
  the 
  quantity 
  of 
  oil 
  exceeds 
  that 
  required 
  for 
  the 
  

   formation 
  of 
  the 
  mono-molecular 
  layer, 
  and 
  he 
  formulates 
  a 
  

   conclusion, 
  not 
  accepted 
  by 
  Marcelin, 
  that 
  the 
  thickness 
  of 
  

   the 
  layer 
  depends 
  upon 
  the 
  existence 
  and 
  dimensions 
  of 
  the 
  

   globules 
  into 
  which 
  most 
  of 
  the 
  superfluous 
  oil 
  is 
  collected, 
  

   inasmuch 
  as 
  experiment 
  proves 
  that 
  when 
  a 
  layer 
  with 
  fine 
  

   globules 
  exists 
  beside 
  a 
  layer 
  with 
  large 
  globules, 
  the 
  former 
  

   always 
  contracts 
  at 
  the 
  expense 
  of 
  the 
  latter. 
  As 
  to 
  this, 
  it 
  

   may 
  be 
  worth 
  notice 
  that 
  the 
  tension 
  T 
  of 
  the 
  contaminated 
  

   surface 
  could 
  not 
  be 
  expressed 
  as 
  a 
  function 
  merely 
  of 
  the 
  

   volume 
  of 
  the 
  drop 
  and 
  of 
  the 
  two 
  other 
  tensions, 
  viz. 
  T 
  1 
  

   the 
  tension 
  of 
  an 
  air-oil 
  surface 
  and 
  T 
  2 
  that 
  of 
  a 
  water-oil 
  

   surface. 
  It 
  would 
  be 
  necessary 
  to 
  introduce 
  other 
  quantities, 
  

   such 
  as 
  gravity, 
  or 
  molecular 
  dimensions. 
  I 
  am 
  still 
  of 
  the 
  

   opinion 
  formerly 
  expressed 
  that 
  these 
  complications 
  are 
  

   the 
  result 
  of 
  impurity 
  in 
  the 
  oil. 
  If 
  the 
  oil 
  were 
  really 
  

   homogeneous, 
  Devaux' 
  views 
  would 
  lead 
  one 
  to 
  regard 
  the 
  

   continued 
  existence 
  of 
  two 
  sizes 
  of 
  globules 
  on 
  the 
  same 
  

   surface 
  as 
  impossible. 
  What 
  would 
  there 
  be 
  to 
  hinder 
  the 
  

   rapid 
  growth 
  of 
  the 
  smaller 
  at 
  the 
  expense 
  of 
  the 
  greater 
  

   until 
  equality 
  was 
  established 
  ? 
  On 
  the 
  other 
  hand, 
  an 
  

   impurity, 
  present 
  only 
  in 
  small 
  proportion, 
  would 
  naturally 
  

   experience 
  more 
  difficulty 
  in 
  finding 
  its 
  way 
  about. 
  

  

  The 
  importance 
  of 
  impurities 
  in 
  influencing 
  the 
  transfor- 
  

   mations 
  of 
  oil-films 
  was 
  insisted 
  on 
  long 
  ago 
  by 
  Tomlinson 
  § 
  ; 
  

  

  * 
  A 
  summary 
  of 
  Devaux' 
  work, 
  dating- 
  from 
  1903 
  onwards, 
  will 
  be 
  

   found 
  in 
  the 
  Revue 
  Gen. 
  d. 
  Sciences 
  for 
  Feb. 
  28, 
  1913. 
  

   t 
  Annates 
  d. 
  Physique, 
  t. 
  i. 
  p. 
  19 
  (1914). 
  

   t 
  Proc. 
  Roy. 
  Soc. 
  A, 
  vol. 
  Lraviii. 
  p. 
  319 
  (1913). 
  

   § 
  Phil. 
  Mag. 
  vol. 
  xxvi. 
  p. 
  187 
  (1863). 
  

  

  