﻿Minute 
  Metal 
  Particles 
  for 
  Ligltt-waves. 
  405 
  

  

  the 
  application 
  of 
  cold, 
  and 
  remain 
  so 
  permanently. 
  What 
  was 
  

   still 
  more 
  remarkable, 
  the 
  appearance 
  o£ 
  the 
  spot 
  viewed 
  in 
  

   reflected 
  light 
  indicated 
  clearly 
  that 
  the 
  size 
  of 
  the 
  particles 
  

   had 
  been 
  increased, 
  the 
  spot 
  showing 
  the 
  silky 
  lustre 
  to 
  which 
  

   I 
  have 
  already 
  alluded, 
  while 
  the 
  film 
  surrounding 
  it 
  scattered 
  

   no 
  light 
  at 
  all. 
  I 
  had 
  noticed 
  that 
  these 
  films 
  were 
  apparently 
  

   made 
  up 
  of 
  two 
  sets 
  of 
  particles 
  — 
  one 
  set 
  large 
  enough 
  to 
  be 
  

   seen 
  under 
  a 
  low 
  power, 
  the 
  other 
  only 
  coming 
  into 
  view 
  

   under 
  the 
  highest 
  power 
  obtainable. 
  After 
  the 
  temperature 
  

   change, 
  the 
  smaller 
  ones 
  seemed 
  to 
  have 
  disappeared 
  entirely; 
  

   and 
  I 
  am 
  now 
  of 
  the 
  opinion 
  that 
  the 
  condensation 
  of 
  the 
  

   fluid 
  film 
  enabled 
  them 
  in 
  some 
  way 
  to 
  gather 
  about 
  and 
  

   adhere 
  to 
  the 
  larger 
  particles, 
  building 
  up 
  aggregates 
  large 
  

   enough 
  to 
  diffuse 
  light. 
  

  

  Changes 
  produced 
  by 
  Oxidation. 
  

  

  If 
  the 
  tip 
  of 
  one 
  of 
  the 
  bulbs 
  is 
  cut 
  off, 
  the 
  entrance 
  of 
  the 
  

   air 
  causes 
  the 
  coloured 
  film 
  to 
  vanish 
  like 
  a 
  flash. 
  In 
  some 
  

   instances, 
  I 
  was 
  of 
  the 
  impression 
  that 
  I 
  detected 
  a 
  momentary 
  

   change 
  of 
  colour 
  before 
  the 
  film 
  disappeared. 
  To 
  lengthen 
  

   the 
  process, 
  1 
  adopted 
  the 
  expedient 
  of 
  drawing 
  the 
  end 
  of 
  

   the 
  bulb 
  out 
  into 
  a 
  long 
  fine 
  capillary, 
  with 
  a 
  bore 
  less 
  than 
  

   one 
  one-hundredth 
  of 
  a 
  millimetre. 
  In 
  this 
  bulb 
  a 
  film 
  of 
  a 
  

   deep 
  pink 
  colour 
  was 
  formed, 
  and 
  on 
  cutting 
  off 
  the 
  tip 
  of 
  

   the 
  capillary 
  the 
  colour 
  changed 
  to 
  blue, 
  and 
  the 
  film 
  vanished 
  

   almost 
  immediately. 
  The 
  small 
  amount 
  of 
  air 
  necessary 
  to 
  

   efface 
  the 
  films 
  is 
  indicated 
  by 
  the 
  fact 
  that 
  at 
  the 
  end 
  of 
  an 
  

   hour 
  there 
  was 
  still 
  a 
  fairly 
  good 
  vacuum 
  in 
  the 
  bulb, 
  not- 
  

   withstanding 
  the 
  fact 
  that 
  the 
  end 
  of 
  the 
  capillary 
  had 
  been 
  

   open 
  all 
  the 
  while. 
  If 
  the 
  mouth 
  of 
  the 
  capillary 
  is 
  fused 
  

   immediately 
  after 
  the 
  oxidation 
  of 
  the 
  film, 
  a 
  new 
  coloured 
  

   film 
  can 
  be 
  formed 
  by 
  heating 
  the 
  metal, 
  the 
  oxygen 
  having 
  

   been 
  removed 
  by 
  the 
  first 
  film. 
  This 
  process 
  can 
  be 
  repeated 
  

   a 
  number 
  of 
  times, 
  showing 
  that 
  the 
  presence 
  of 
  the 
  oxide 
  on 
  

   the 
  glass 
  does 
  not 
  interfere 
  with 
  the 
  deposition 
  of 
  the 
  coloured 
  

   film. 
  If 
  the 
  process 
  of 
  oxidation 
  be 
  made 
  very 
  slow, 
  by 
  

   employing 
  a 
  very 
  long 
  capillary, 
  and 
  the 
  process 
  watched 
  

   under 
  the 
  microscope, 
  the 
  black 
  particles 
  slowly 
  become 
  dim, 
  

   and 
  finally 
  fade 
  away. 
  I 
  am 
  of 
  the 
  opinion 
  that 
  the 
  micro- 
  

   scope 
  merely 
  shows 
  us 
  the 
  diffraction-disk 
  due 
  to 
  the 
  opaque 
  

   particle. 
  This 
  would 
  become 
  dimmer 
  as 
  the 
  size 
  of 
  the 
  

   particle 
  is 
  reduced, 
  without 
  any 
  apparent 
  change 
  of 
  size. 
  

   Examination 
  with 
  the 
  spectroscope 
  shows 
  us 
  that, 
  during 
  the 
  

   process 
  of 
  oxidation, 
  the 
  absorption-band 
  sometimes 
  moves 
  out 
  

   of 
  the 
  spectrum 
  through 
  the 
  red 
  end, 
  and 
  sometimes 
  merely 
  

   fades 
  away 
  without 
  any 
  motion. 
  I 
  have 
  tried 
  filling 
  the 
  

  

  