﻿462 
  

  

  Prof. 
  0. 
  W. 
  Richardson 
  on 
  the 
  

  

  Thus 
  when 
  a 
  fresh 
  specimen 
  of 
  calcium 
  iodide 
  is 
  heated 
  at 
  

   a 
  low 
  temperature 
  practically 
  all 
  the 
  negative 
  emission 
  is 
  

   carried 
  by 
  heavy 
  ions 
  and 
  the 
  proportion 
  of 
  negative 
  electrons 
  

   present 
  is 
  negligible. 
  

  

  Measurements 
  of 
  e/m 
  for 
  the 
  heavy 
  negative 
  ions 
  both 
  by 
  

   the 
  slit 
  and 
  balance 
  methods 
  were 
  made 
  under 
  these 
  conditions 
  

   at 
  H25°, 
  when 
  the 
  proportion 
  of 
  negative 
  electrons 
  present 
  

   was 
  negligible. 
  The 
  results 
  are 
  shown 
  in 
  the 
  following- 
  

   table 
  : 
  — 
  

  

  Table 
  I. 
  

  

  Method. 
  

  

  Balance. 
  

  

  Balance. 
  

  

  Balance. 
  

  

  Slit. 
  

  

  -2x 
  

  

  4-10 
  

   85 
  

   113 
  

  

  4-01 
  

   82 
  

   119 
  

  

  400 
  

   81 
  

   119 
  

  

  3-85 
  

  

  75 
  

   128 
  

  

  e/m 
  

  

  m/H 
  

  

  

  The 
  mean 
  value 
  of 
  m/E. 
  is 
  120. 
  This 
  is 
  not 
  very 
  different 
  

   from 
  the 
  chemical 
  equivalent 
  weight 
  of 
  I_, 
  viz. 
  127. 
  Thus 
  the 
  

   heavy 
  ions 
  given 
  off 
  by 
  calcium 
  iodide 
  at 
  low 
  temperatures 
  are 
  

   atoms 
  of 
  iodine 
  combined 
  with 
  a 
  single 
  electron. 
  The 
  above 
  

   values 
  of 
  e/m 
  and 
  m/H 
  were 
  confirmed 
  by 
  other 
  measure- 
  

   ments 
  in 
  which 
  the 
  applied 
  electrostatic 
  field 
  was 
  82 
  and 
  

   40 
  volts 
  respectively 
  instead 
  of 
  200, 
  and 
  there 
  is 
  every 
  reason 
  

   to 
  believe 
  they 
  are 
  correct. 
  This 
  is 
  important 
  because, 
  as 
  

   we 
  shall 
  see 
  later, 
  unexpected 
  difficulties 
  have 
  arisen 
  in 
  

   determining 
  e/m 
  and 
  m/H 
  for 
  the 
  heavy 
  negative 
  ions 
  which 
  

   are 
  present 
  in 
  other 
  cases. 
  

  

  When 
  the 
  salt 
  had 
  got 
  into 
  a 
  steady 
  state 
  at 
  400°, 
  so 
  that 
  

   the 
  emission 
  varied 
  very 
  little 
  with 
  the 
  time, 
  measurements 
  

   of 
  the 
  current 
  with 
  different 
  applied 
  negative 
  potentials 
  

   up 
  to 
  —200 
  were 
  made, 
  both 
  with 
  the 
  magnetic 
  field 
  on 
  and 
  

   off. 
  The 
  resulting 
  current-E.M.F. 
  curves 
  which 
  are 
  shown 
  

   in 
  fig. 
  2 
  are 
  not 
  very 
  different 
  from 
  those 
  given 
  by 
  "the 
  

   positive 
  emission 
  from 
  most 
  salts 
  under 
  conditions 
  which 
  are 
  

   the 
  same 
  except 
  for 
  the 
  different 
  sign 
  of 
  the 
  potential. 
  The 
  

   o.ily 
  important 
  difference 
  is 
  the 
  increase 
  in 
  the 
  current 
  

   between 
  160 
  and 
  200 
  volts 
  when 
  the 
  electrons 
  are 
  present, 
  

   which 
  may 
  perhaps 
  be 
  due 
  to 
  ionization 
  by 
  collisions. 
  

  

  The 
  variation 
  of 
  the 
  two 
  kinds 
  of 
  emission 
  with 
  time 
  when 
  

   the 
  salt 
  was 
  kept 
  at 
  a 
  constant 
  temperature 
  was 
  next 
  

   examined. 
  A 
  speck 
  of 
  the 
  salt 
  about 
  "005 
  cm. 
  2 
  in 
  area 
  was 
  

  

  