﻿Lime 
  for 
  the 
  Wehnelt 
  Cathode. 
  597 
  

  

  tinned, 
  the 
  current 
  obtained 
  on 
  again 
  closing 
  the 
  discharge 
  

   circuit 
  was 
  in 
  every 
  case 
  smaller 
  than 
  it 
  was 
  just 
  before 
  break- 
  

   ing. 
  This 
  is 
  shown 
  by 
  fig. 
  5. 
  The 
  behavior 
  of 
  the 
  lime 
  seemed 
  

   to 
  be 
  much 
  the 
  same 
  as 
  though 
  it 
  had 
  been 
  allowed 
  to 
  stand 
  in 
  

   the 
  cold, 
  except 
  that 
  the 
  effect 
  was 
  not 
  so 
  pronounced. 
  This 
  

   shows 
  that 
  the 
  decrease 
  in 
  activity 
  for 
  short 
  intervals 
  of 
  no 
  dis- 
  

   charge 
  was 
  slight, 
  yet 
  definite, 
  if 
  the 
  lime 
  was 
  kept 
  hot. 
  This 
  

   result 
  does 
  not 
  agree 
  with 
  that 
  of 
  Willows 
  and 
  Picton, 
  who 
  

   observed, 
  for 
  the 
  salts 
  that 
  they 
  used, 
  a 
  decided 
  increase 
  in 
  

   activity 
  under 
  the 
  same 
  conditions. 
  

  

  Data 
  on 
  the 
  saturation 
  voltage 
  were 
  obtained 
  as 
  follows 
  : 
  for 
  

   a 
  given 
  heating 
  current 
  and 
  a 
  discharge 
  voltage 
  of 
  40 
  volts 
  

   the 
  run 
  was 
  continued 
  until 
  the 
  current 
  became 
  steady, 
  after 
  

   which 
  the 
  voltage 
  was 
  advanced 
  by 
  steps 
  of 
  40 
  volts 
  at 
  inter- 
  

   vals 
  of 
  10 
  minutes, 
  the 
  maximum 
  current 
  being 
  recorded 
  each 
  

   time. 
  The 
  curve 
  in 
  fig. 
  6 
  shows 
  the 
  results 
  obtained. 
  There 
  

   was 
  saturation 
  at 
  200 
  volts. 
  

  

  The 
  Bank 
  of 
  England 
  wax 
  upon 
  analysis 
  was 
  found 
  to 
  have 
  

   the 
  following 
  principal 
  constituents 
  : 
  calcium 
  sulphate 
  (gyp- 
  

   sum), 
  barium 
  sulphate 
  (heavy 
  spar), 
  mercuric 
  sulphide 
  (cinna- 
  

   bar), 
  and 
  shellac. 
  

  

  Summary. 
  

  

  It 
  was 
  shown 
  that 
  when 
  Bank 
  of 
  England 
  sealing 
  wax 
  is 
  used 
  

   as 
  the 
  source 
  of 
  lime 
  there 
  is 
  a 
  falling 
  off 
  in 
  the 
  activity 
  

   with 
  time. 
  

  

  When 
  a 
  maximum 
  is 
  reached 
  most 
  of 
  the 
  electrons 
  are 
  

   emitted 
  during 
  the 
  first 
  run. 
  

  

  When 
  the 
  discharge 
  is 
  broken 
  while 
  the 
  heating 
  current 
  is 
  

   maintained 
  there 
  is 
  a 
  slight 
  falling 
  off 
  in 
  the 
  negative 
  stream. 
  

  

  The 
  above 
  results 
  are 
  exactly 
  opposite 
  to 
  those 
  obtained 
  by 
  

   Willows 
  and 
  Picton 
  using 
  calcium 
  oxide 
  on 
  a 
  platinum 
  strip, 
  

   while 
  they 
  agree 
  in 
  part 
  with 
  the 
  observations 
  of 
  S 
  heard, 
  who 
  

   found 
  that 
  the 
  activity 
  for 
  cadmium 
  iodide 
  and 
  iodine, 
  with 
  

   the 
  tube 
  method, 
  decreased 
  during 
  any 
  given 
  run. 
  

  

  The 
  saturation 
  voltage 
  was 
  found 
  to 
  be 
  200 
  volts. 
  

  

  There 
  was 
  a 
  falling 
  off 
  in 
  the 
  maxima 
  for 
  successive 
  runs, 
  

   and 
  the 
  steady 
  current 
  for 
  any 
  given 
  run 
  was 
  usually 
  much 
  

   smaller 
  than 
  that 
  for 
  the 
  preceding 
  run 
  with 
  the 
  same 
  lime. 
  

  

  In 
  conclusion, 
  the 
  writer 
  takes 
  pleasure 
  in 
  thanking 
  Profes- 
  

   sor 
  A. 
  P. 
  Carman 
  for 
  the 
  facilities 
  of 
  the 
  department, 
  and 
  Dr. 
  

   C. 
  T. 
  Knipp 
  for 
  suggesting 
  the 
  problem 
  and 
  assistance 
  in 
  car- 
  

   rying 
  out 
  the 
  details 
  of 
  this 
  investigation. 
  

  

  Physical 
  Laboratory. 
  

  

  University 
  of 
  Illinois. 
  

  

  