﻿through 
  the 
  Gases 
  HCl, 
  HBr, 
  and 
  HI. 
  

  

  471 
  

  

  \vitli 
  a 
  feeble 
  green 
  phosphorescent 
  light 
  that 
  seems 
  to 
  radiate 
  

   from 
  the 
  cathode. 
  

  

  The 
  stability 
  of 
  the 
  different 
  forms 
  of 
  discharge 
  depends 
  

   on 
  pressure 
  and 
  the 
  size 
  of 
  the 
  electrodes. 
  When 
  other 
  

   circumstances 
  are 
  the 
  same 
  the 
  interval 
  for 
  a 
  uniform 
  dis- 
  

   charge 
  is 
  greater 
  for 
  a 
  greater 
  pressure. 
  With 
  a 
  tube 
  of 
  

   exactly 
  the 
  same 
  shape 
  and 
  size, 
  but 
  with 
  electrode-surfaces 
  

   about 
  O'i 
  cm.^, 
  it 
  was 
  found 
  that 
  the 
  uniform 
  as 
  well 
  as 
  the 
  

   striated 
  type 
  for 
  pressures 
  below 
  1*5 
  mm. 
  was 
  very 
  unstable. 
  

   The 
  uniform 
  discharge 
  could 
  be 
  got 
  when 
  fresh 
  gas 
  was 
  

   introduced 
  or 
  when 
  the 
  tube 
  had 
  been 
  " 
  resting 
  '' 
  over 
  night 
  ; 
  

   but 
  if 
  the 
  current 
  was 
  larger 
  than 
  about 
  2 
  . 
  10~^ 
  amp. 
  stria- 
  

   tions 
  set 
  in, 
  which, 
  however, 
  soon 
  disappeared, 
  and 
  the 
  dark 
  

   type 
  became 
  stable 
  for 
  nearly 
  all 
  currents 
  ; 
  only 
  for 
  the 
  very 
  

   smallest 
  currents 
  that 
  could 
  be 
  made 
  to 
  pass 
  was 
  the 
  uniform 
  

   discharge 
  sometimes 
  obtained. 
  The 
  gradients 
  got 
  with 
  this 
  

   tube 
  for 
  the 
  different 
  types 
  are 
  given 
  in 
  Table 
  II. 
  

  

  Table 
  II. 
  

   HCl. 
  

  

  

  P= 
  

  

  0-2. 
  

  

  1 
  

  

  ;^=04. 
  

  

  -. 
  . 
  ,-:^i-o.^ 
  ^^ 
  ^ 
  

  

  3 
  

  

  ■i 
  

  

  103 
  1 
  

  

  Gm. 
  

  

  0-26 
  

   25-2 
  

  

  9-0 
  

   0-4 
  

  

  0-35 
  

   25-6 
  

  

  11-6 
  r'^7-7 
  

  

  6-6 
  1 
  rc^ 
  ^. 
  

  

  '1-8 
  ";; 
  pO''\ 
  

  

  , 
  ^4: 
  2-3 
  

  

  

  i 
  ^ 
  

  

  D. 
  

  

  U. 
  

  

  S. 
  i 
  D. 
  

  

  u: 
  -i). 
  

  

  

  We 
  see 
  from 
  Tables 
  I. 
  and 
  II. 
  that 
  the 
  average 
  P.G. 
  in 
  the 
  

   positive 
  column 
  is 
  greatest 
  for 
  the 
  uniform 
  and 
  smallest 
  for 
  

   the 
  dark 
  discharge. 
  Thus 
  when 
  the 
  discharge 
  by 
  applying 
  a 
  

   large 
  current 
  is 
  made 
  to 
  change 
  type, 
  the 
  change 
  is 
  always 
  

   accomjyanied 
  hy 
  a 
  fall 
  in 
  the 
  average 
  potential 
  gradient. 
  

  

  Reversibility 
  of 
  the 
  Discharge. 
  

  

  § 
  7. 
  As 
  long 
  as 
  the 
  discharge 
  was 
  maintained 
  in 
  the 
  un- 
  

   striated 
  state 
  the 
  conditions 
  were 
  found 
  to 
  be 
  reversible 
  with 
  

   regard 
  to 
  current, 
  or 
  the 
  distribution 
  of 
  potential 
  does 
  not 
  

   depend 
  on 
  the 
  order 
  of 
  operation. 
  Within 
  these 
  limits 
  the 
  

   tube 
  will 
  possess 
  a 
  certain 
  characteristic 
  curve 
  and 
  the 
  

   potential 
  gradient 
  is 
  expressible 
  as 
  a 
  function 
  of 
  current. 
  

  

  When 
  the 
  discharge 
  in 
  the 
  way 
  described 
  is 
  made 
  to 
  

   assume 
  the 
  striated 
  or 
  dark 
  type, 
  the 
  conditions 
  are 
  no 
  longer 
  

  

  