﻿458 
  Prof. 
  0. 
  VY. 
  Richardson 
  on 
  the 
  

  

  for 
  which 
  m/H 
  = 
  27'5, 
  but 
  on 
  the 
  whole 
  Na 
  + 
  (23) 
  and 
  

   K 
  + 
  (39*1) 
  are 
  perhaps 
  more 
  probable. 
  The 
  heavy 
  ions 
  

   point 
  to 
  the 
  existence 
  of 
  Mn(Jl 
  + 
  (90*4) 
  and 
  possibly 
  also 
  

   Mn 
  + 
  (55). 
  It 
  is 
  to 
  be 
  remembered 
  that 
  owing 
  to 
  the 
  

   rapidity 
  with 
  which 
  the 
  values 
  were 
  changing, 
  it 
  is 
  likely 
  

   that 
  most 
  of 
  the 
  above 
  numbers 
  correspond 
  to 
  mixtures 
  of 
  

   ions 
  having 
  different 
  values 
  of 
  ejm. 
  

  

  2. 
  Negative 
  Ions. 
  

  

  It 
  is 
  well 
  known 
  that 
  most 
  substances, 
  if 
  not 
  all, 
  emit 
  

   negative 
  electrons 
  when 
  they 
  are 
  heated 
  to 
  a 
  sufficiently 
  

   high 
  temperature. 
  Certain 
  salts 
  possess 
  the 
  property 
  of 
  

   emitting 
  negative 
  ions 
  at 
  relatively 
  low 
  temperatures. 
  

   I 
  lind 
  that 
  in 
  addition 
  to 
  the 
  oxides, 
  the 
  following 
  salts 
  have 
  

   this 
  power 
  : 
  — 
  The 
  iodides 
  of 
  calcium, 
  strontium, 
  barium 
  and 
  

   cadmium, 
  calcium 
  fluoride, 
  calcium 
  bromide, 
  manganous 
  

   chloride 
  and 
  ferric 
  chloride. 
  This 
  list 
  is 
  probably 
  not 
  

   exhaustive. 
  In 
  general, 
  the 
  negative 
  ions 
  emitted 
  by 
  these 
  

   substances 
  are 
  not 
  all 
  electrons, 
  but 
  consist 
  of 
  a 
  mixture 
  

   of 
  electrons 
  and 
  heavy 
  ions. 
  Calcium 
  iodide 
  appears 
  to 
  

   exhibit 
  this 
  property 
  in 
  a 
  typical 
  manner, 
  and 
  I 
  have 
  

   examined 
  its 
  behaviour 
  in 
  some 
  detail. 
  

  

  Calcium 
  Iodide. 
  Cal 
  2 
  . 
  

  

  One 
  of 
  the 
  objects 
  of 
  the 
  experiments 
  has 
  been 
  to 
  measure 
  

   the 
  quantity 
  of 
  negative 
  electrons 
  and 
  the 
  quantity 
  of 
  heavy 
  

   negative 
  ions 
  emitted 
  under 
  different 
  conditions. 
  The 
  salt 
  

   was 
  placed 
  on 
  platinum 
  strips, 
  1 
  mm. 
  wide, 
  mounted 
  in 
  the 
  

   apparatus 
  for 
  measuring 
  e\m 
  already 
  referred 
  to. 
  The 
  length 
  

   of 
  the 
  strips 
  was 
  about 
  1*3 
  cm. 
  They 
  were 
  heated 
  until 
  the 
  

   positive 
  emission 
  from 
  the 
  platinum 
  had 
  been 
  got 
  rid 
  of, 
  

   before 
  the 
  calcium 
  iodide 
  was 
  placed 
  on 
  them. 
  The 
  

   apparatus 
  was 
  placed 
  between 
  the 
  jaws 
  of 
  the 
  electromagnet 
  

   in 
  the 
  usual 
  position 
  for 
  determining 
  ejm. 
  The 
  current 
  from 
  

   the 
  strip 
  to 
  the 
  plates, 
  when 
  the 
  strip 
  was 
  maintained 
  at 
  

   a 
  potential 
  of 
  — 
  #0 
  volts 
  with 
  respect 
  to 
  the 
  plates, 
  was 
  

   measured 
  under 
  two 
  different 
  conditions. 
  Under 
  the 
  first 
  

   condition 
  a 
  small 
  current 
  flowed 
  through 
  the 
  windings 
  of 
  the 
  

   electromagnet, 
  so 
  that 
  there 
  was 
  a 
  magnetic 
  field 
  large 
  

   enough 
  to 
  stop 
  the 
  electrons 
  from 
  reaching 
  the 
  plate, 
  but 
  

   not 
  large 
  enough 
  to 
  stop 
  any 
  of 
  the 
  heavy 
  ions. 
  The 
  proper 
  

   magnetic 
  field 
  to 
  use 
  was 
  found 
  by 
  separate 
  experiments 
  

   on 
  the 
  negative 
  emission 
  from 
  a 
  hot 
  platinum 
  strip 
  without 
  

   any 
  salt 
  on 
  it. 
  In 
  these 
  experiments 
  I 
  was 
  not 
  able 
  to 
  

   detect 
  any 
  emission 
  of 
  heavy 
  ions, 
  all 
  the 
  negative 
  ions 
  

  

  