﻿obtaining 
  Coloured 
  Flames 
  of 
  Great 
  Intensity. 
  

  

  387 
  

  

  be 
  admitted 
  and 
  the 
  combustion 
  of 
  the 
  coal 
  gas 
  thereby 
  

   rendered 
  more 
  complete, 
  the 
  luminosity 
  of 
  the 
  flame 
  above 
  

   the 
  oxygen 
  path 
  gradually 
  decreases 
  and 
  finally 
  becomes 
  

   less 
  than 
  that 
  of 
  the 
  region 
  below, 
  as 
  sketched 
  in 
  fig. 
  4. 
  In 
  

  

  Fio-. 
  4. 
  

  

  Excess 
  of 
  Air. 
  

  

  fact, 
  when 
  viewed 
  in 
  the 
  direction 
  of 
  the 
  oxygen 
  path, 
  the 
  

   luminosity 
  along 
  and 
  above 
  it 
  is 
  found 
  to 
  have 
  been 
  com- 
  

   pletely 
  arrested, 
  the 
  reduced 
  light 
  as 
  seen 
  sideways 
  being 
  

   merely 
  due 
  to 
  the 
  thin 
  borders 
  of 
  flame 
  rising 
  up 
  on 
  either 
  

   side 
  of 
  the 
  oxygen 
  stream. 
  That 
  the 
  extinction 
  of 
  the 
  

   luminous 
  vibrations 
  in 
  this 
  case 
  is 
  caused 
  principally 
  by 
  

   actual 
  cooling 
  of 
  the 
  vapour 
  and 
  not 
  merely 
  by 
  oxidation, 
  is 
  

   shown 
  by 
  the 
  fact 
  that 
  when 
  a 
  stream 
  of: 
  nitrogen 
  is 
  passed 
  

   into 
  the 
  flame 
  the 
  same 
  extinction 
  is 
  observed. 
  On 
  the 
  other 
  

   hand, 
  a 
  stream 
  of 
  ammonia 
  does 
  not 
  reduce 
  the 
  intensity 
  of 
  the 
  

   light 
  emission 
  in 
  the 
  upper 
  zone 
  ; 
  the 
  feebly 
  luminous 
  flame 
  

   with 
  which 
  the 
  ammonia 
  burns 
  as 
  it 
  passes 
  through 
  the 
  air-coal 
  

   gas 
  flame 
  seems 
  to 
  be 
  just 
  sufficient 
  to 
  keep 
  up 
  the 
  tempe- 
  

   rature 
  of 
  the 
  latter. 
  Also 
  when 
  a 
  high 
  temperature 
  oxy-coal 
  

   gas 
  flame 
  is 
  directed 
  through 
  the 
  air-coal 
  gas 
  flame 
  under 
  

   these 
  conditions, 
  the 
  portion 
  of 
  the 
  latter 
  situated 
  above 
  the 
  

   path 
  of 
  the 
  oxy-coal 
  gas 
  flame 
  remains 
  always 
  a 
  little 
  

   brighter. 
  All 
  the 
  above 
  observations 
  were 
  made 
  on 
  the 
  

   luminous 
  vapours 
  of 
  sodium, 
  strontium, 
  lithium, 
  calcium, 
  and 
  

   barium. 
  

  

  Summary. 
  

  

  The 
  series 
  of 
  observations 
  recorded 
  in 
  this 
  note 
  clearly 
  

   shows 
  that 
  the 
  role 
  of 
  the 
  oxygen 
  in 
  Talbot's 
  experiment 
  is 
  

   to 
  increase 
  the 
  rate 
  of 
  combustion 
  of 
  the 
  unburnt 
  oases 
  in 
  

  

  