﻿384 
  Mr. 
  G. 
  A. 
  Hemsalech 
  on 
  Fox 
  Talbot's 
  Method 
  of 
  

  

  brass 
  plate, 
  \ 
  inch 
  thick, 
  having 
  49 
  one-millimetre 
  holes 
  per 
  

   square 
  centimetre. 
  Experiments 
  were 
  made 
  with 
  the 
  salts 
  

   of 
  sodium 
  and 
  calcium. 
  The 
  greatest 
  intensity 
  of 
  the 
  metal 
  

   vapour 
  emission 
  was 
  also 
  in 
  this 
  case 
  obtained 
  when 
  the 
  salts 
  

   were 
  held 
  near 
  the 
  base 
  of 
  the 
  flame 
  or 
  placed 
  on 
  the 
  per- 
  

   forated 
  plate. 
  When 
  the 
  oxygen 
  was 
  passed 
  through 
  the 
  

   luminous 
  vapour 
  in 
  the 
  region 
  above 
  the 
  salt, 
  about 
  half 
  way 
  

   up 
  the 
  flame, 
  the 
  brightening 
  along 
  the 
  oxygen 
  path 
  was 
  

   relatively 
  feeble; 
  but 
  when 
  now 
  the 
  salt 
  was 
  raised 
  and 
  held 
  

   in 
  the 
  path 
  of 
  the 
  oxygen, 
  the 
  intensity 
  again 
  was 
  fairly 
  

   great, 
  though 
  much 
  less 
  so 
  than 
  when 
  both 
  the 
  stream 
  of 
  

   oxygen 
  and 
  the 
  salt 
  were 
  close 
  to 
  the 
  explosion 
  region. 
  On 
  

   the 
  other 
  hand, 
  near 
  the 
  tip 
  of 
  the 
  flame, 
  where 
  combustion 
  

   of 
  the 
  gases 
  is 
  nearly 
  complete, 
  no 
  luminous 
  effect 
  was 
  ob- 
  

   served 
  when 
  oxygen 
  was 
  blown 
  against 
  the 
  salt. 
  Thus 
  the 
  

   oxygen, 
  in 
  order 
  to 
  be 
  effective 
  by 
  this 
  method, 
  must 
  be 
  

   directed 
  upon 
  the 
  substance 
  to 
  be 
  vaporized 
  in 
  the 
  presence 
  

   of 
  unburnt 
  gases 
  (hydrocarbons 
  and 
  hydrogen). 
  This 
  fact 
  

   is 
  further 
  illustrated 
  by 
  the 
  following 
  observations, 
  which 
  at 
  

   the 
  same 
  time 
  prove 
  that 
  the 
  light 
  effect 
  obtained 
  in 
  Talbot's 
  

   experiment 
  is 
  not 
  due 
  to 
  mere 
  combustion 
  of 
  the 
  material 
  

   placed 
  on 
  the 
  wick 
  : 
  when 
  the 
  salt 
  is 
  held 
  in 
  the 
  flame 
  near 
  

   the 
  border, 
  and 
  the 
  oxygen 
  enters 
  from 
  the 
  opposite 
  side 
  

   (fig. 
  1) 
  in 
  such 
  a 
  way 
  that 
  it 
  traverses 
  a 
  long 
  zone 
  of 
  flame 
  

  

  Fig. 
  1. 
  

  

  Maximum 
  Effect. 
  

  

  containing 
  unburnt 
  gases 
  before 
  encountering 
  the 
  salt, 
  the 
  

   luminous 
  effect 
  is 
  a 
  maximum. 
  If, 
  however, 
  the 
  salt 
  be 
  held 
  

   near 
  to 
  the 
  point 
  of 
  the 
  border 
  at 
  which 
  the 
  oxygen 
  enters, 
  

   no 
  effect 
  is 
  observed 
  (fig. 
  2). 
  

  

  