﻿Electrons 
  from 
  Tungsten 
  at 
  High 
  Temperatures. 
  347 
  

  

  getting 
  rid 
  o£ 
  the 
  absorbed 
  gases 
  and 
  volatile 
  impurities 
  

   which 
  form 
  such 
  a 
  persistent 
  source 
  of 
  difficulties 
  in 
  experi- 
  

   ments 
  of 
  this 
  character. 
  Unless 
  some 
  such 
  treatment 
  is 
  

   resorted 
  to, 
  the 
  metal 
  electrodes 
  and 
  glass 
  walls 
  of 
  these 
  

   tubes 
  continue 
  to 
  give 
  off 
  relatively 
  large 
  amounts 
  of 
  gas 
  

   under 
  the 
  influence 
  of 
  the 
  heat 
  radiated 
  from 
  the 
  filaments, 
  

   and 
  it 
  has 
  always 
  been 
  possible 
  that 
  this 
  evolution 
  of 
  gas 
  

   might 
  have 
  played 
  an 
  important 
  part 
  in 
  the 
  electronic 
  emis- 
  

   sion. 
  The 
  mode 
  of 
  treatment 
  used, 
  for 
  which 
  I 
  am 
  largely 
  

   indebted 
  to 
  the 
  experience 
  and 
  suggestions 
  of 
  Dr. 
  Irving 
  

   Langmuir, 
  of 
  the 
  General 
  Electric 
  Company's 
  Research 
  

   Laboratory 
  at 
  Schenectady, 
  N.Y., 
  seems 
  very 
  superior 
  to 
  

   anything 
  in 
  this 
  direction 
  which 
  has 
  previously 
  been 
  

   published. 
  

  

  Tests 
  have 
  been 
  carried 
  out 
  covering 
  the 
  alternative 
  hypo- 
  

   theses, 
  as 
  to 
  the 
  possible 
  mode 
  of 
  origin 
  of 
  the 
  electronic 
  

   emission, 
  which 
  are 
  enumerated 
  below: 
  

  

  (1) 
  The 
  emission 
  is 
  due 
  to 
  the 
  evolution 
  of 
  gas 
  by 
  the 
  

   filaments. 
  

  

  The 
  lamp 
  and 
  McLeod 
  gauge 
  were 
  cut 
  off 
  from 
  the 
  rest 
  

   of 
  the 
  apparatus 
  by 
  means 
  of 
  a 
  mercury 
  trap, 
  the 
  volume 
  

   being 
  then 
  approximately 
  600 
  c.c. 
  A 
  filament 
  4 
  cm. 
  long, 
  

   giving 
  a 
  thermionic 
  current 
  of 
  "064 
  amp., 
  was 
  found 
  to 
  

   increase 
  the 
  pressure 
  from 
  zero 
  to 
  < 
  1 
  x 
  10" 
  6 
  mm. 
  in 
  five 
  

   minutes. 
  The 
  number 
  of 
  molecules 
  N-, 
  of 
  gas 
  given 
  off 
  is 
  

   therefore 
  2*13 
  x 
  10 
  13 
  . 
  The 
  number 
  of 
  electrons 
  given 
  off 
  is 
  

   N 
  2 
  = 
  l*2xl0 
  20 
  . 
  The 
  number 
  of 
  electrons 
  emitted 
  for 
  each 
  

   molecule 
  of 
  gas 
  evolved 
  is 
  thus 
  N 
  2 
  /N 
  1 
  >5*64x 
  10 
  6 
  . 
  

  

  In 
  the 
  above 
  experiment 
  a 
  liquid-air 
  trap 
  was 
  interposed 
  to 
  

   keep 
  the 
  mercury 
  vapour 
  off 
  the 
  filament. 
  In 
  another 
  ex- 
  

   periment 
  with 
  a 
  filament 
  8 
  cm. 
  long 
  this 
  was 
  not 
  the 
  case, 
  

   and 
  with 
  a 
  current 
  of 
  *050 
  amp. 
  the 
  pressure 
  rose 
  in 
  thirty 
  

   minutes 
  to 
  a 
  value 
  which 
  was 
  too 
  small 
  to 
  measure, 
  but 
  

   w 
  T 
  hich 
  was 
  estimated 
  as 
  less 
  than 
  10 
  ~ 
  7 
  mm. 
  The 
  corre- 
  

   sponding 
  value 
  of 
  N 
  2 
  /^i 
  is 
  2*6 
  xlO 
  8 
  . 
  In 
  this 
  case 
  the 
  

   current 
  was 
  unaffected 
  when 
  the 
  mercury 
  vapour 
  was 
  sub- 
  

   sequently 
  cut 
  off 
  by 
  liquid 
  air 
  (a 
  change 
  of 
  0*4 
  per 
  cent, 
  

   would 
  have 
  been 
  detected). 
  

  

  The 
  magnitude 
  of 
  the 
  above 
  numbers 
  effectually 
  disposes 
  

   of 
  the 
  idea 
  that 
  the 
  emission 
  has 
  anything 
  to 
  do 
  with 
  the 
  

   evolution 
  of 
  gas. 
  

  

  (2) 
  The 
  emission 
  is 
  caused 
  by 
  chemical 
  action 
  or 
  some 
  

   other 
  cause 
  depending 
  on 
  impacts 
  between 
  the 
  - 
  gas 
  molecules 
  

   and 
  the 
  filaments. 
  

  

  In 
  a 
  tube 
  with 
  a 
  filament 
  1*4 
  cm. 
  in 
  length 
  and 
  having 
  

   1*65 
  x 
  10~ 
  2 
  cm. 
  2 
  superficial 
  area, 
  the 
  pressure 
  rose 
  to 
  

  

  2 
  A 
  2 
  

  

  