﻿

  

  Ions 
  from 
  Hot 
  Salts. 
  459 
  

  

  given 
  off 
  by 
  the 
  hot 
  platinum 
  being 
  electrons. 
  This 
  

   supports 
  the 
  recently 
  published 
  observations 
  of 
  Owen 
  and 
  

   Halsall 
  *. 
  

  

  in 
  the 
  second 
  case 
  the 
  current 
  to 
  the 
  plates 
  was 
  measured 
  

   when 
  there 
  was 
  no 
  current 
  through 
  the 
  windings 
  of 
  the 
  

   electromagnet. 
  In 
  this 
  case 
  the 
  ions 
  are 
  only 
  subject 
  to 
  

   the 
  residual 
  field 
  of 
  the 
  electromagnet 
  and 
  the 
  field 
  due 
  

   to 
  the 
  heating 
  current 
  in 
  the 
  strip. 
  As 
  the 
  current 
  was 
  

   approximately 
  saturated 
  under 
  these 
  conditions, 
  these 
  fields 
  

   are 
  too 
  small 
  to 
  stop 
  even 
  the 
  electrons 
  from 
  getting 
  across. 
  

   It 
  will 
  be 
  seen 
  that 
  the 
  first 
  measurement 
  gives 
  the 
  quantity 
  

   of 
  electricity 
  which 
  is 
  carried 
  away 
  from 
  the 
  strip 
  in 
  the 
  

   form 
  of 
  heavy 
  ions, 
  and 
  the 
  second 
  the 
  total 
  amount 
  which 
  

   is 
  carried 
  away 
  both 
  by 
  the 
  heavy 
  ions 
  and 
  by 
  the 
  electrons. 
  

  

  The 
  first 
  measurements 
  were 
  made 
  with 
  the 
  object 
  of 
  

   finding 
  how 
  the 
  magnitude 
  and 
  relative 
  proportion 
  of 
  these 
  

   emissions 
  varied 
  with 
  the 
  temperature 
  of 
  the 
  salt. 
  The 
  

   wdiole 
  of 
  the 
  strip 
  was 
  covered 
  with 
  the 
  salt. 
  The 
  tempera- 
  

   tures 
  given 
  are 
  platinum 
  temperatures, 
  and 
  were 
  deduced 
  

   from 
  the 
  resistance 
  of 
  the 
  strip. 
  The 
  results 
  are 
  intended 
  

   only 
  as 
  a 
  rough 
  indication, 
  and 
  no 
  great 
  accuracy 
  is 
  claimed 
  

   for 
  them. 
  In 
  fact, 
  the 
  phenomena 
  cannot 
  be 
  represented 
  as 
  

   a 
  function 
  of 
  temperature 
  in 
  this 
  way 
  since, 
  as 
  will 
  be 
  

   shown 
  below, 
  the 
  magnitude 
  of 
  the 
  emission 
  varies 
  very 
  

   rapidly 
  with 
  the 
  time 
  when 
  the 
  temperature 
  of 
  the 
  sait 
  is 
  

   kept 
  constant. 
  The 
  numbers 
  in 
  the 
  following 
  table 
  (p. 
  460) 
  

   were 
  obtained 
  by 
  taking 
  a 
  series 
  of 
  measurements 
  as 
  rapidly 
  

   as 
  possible. 
  Row 
  1 
  gives 
  the 
  platinum 
  resistance 
  tempe- 
  

   rature, 
  row 
  2 
  the 
  current 
  in 
  amperes 
  carried 
  by 
  heavy 
  ions, 
  

   row 
  3 
  the 
  current 
  in 
  amperes 
  carried 
  by 
  heavy 
  ions 
  and 
  

   electrons 
  together, 
  and 
  row 
  4 
  the 
  proportion 
  of 
  the 
  whole 
  

   current 
  which 
  is 
  carried 
  by 
  electrons. 
  

  

  These 
  measurements 
  were 
  not 
  made 
  with 
  an 
  entirely 
  

   fresh 
  specimen 
  of 
  the 
  salt, 
  but 
  with 
  one 
  wdiich 
  had 
  been 
  

   heated 
  for 
  several 
  hours 
  at 
  400°. 
  Otherwise 
  the 
  results 
  

   would 
  have 
  been 
  different 
  in 
  some 
  important 
  particulars. 
  

   The 
  numbers 
  also 
  are 
  somewhat 
  irregular 
  owing- 
  to 
  the 
  

   combined 
  effect 
  of 
  the 
  temperature 
  and 
  time 
  changes. 
  

   However, 
  they 
  bear 
  out 
  the 
  following 
  conclusions 
  which 
  

   I 
  have 
  amply 
  confirmed 
  by 
  other 
  experiments 
  : 
  — 
  

  

  There 
  is 
  a 
  surprisingly 
  large 
  emission 
  of 
  negative 
  ions 
  

   from 
  calcium 
  iodide 
  at 
  comparatively 
  low 
  temperatures. 
  

   This 
  property 
  is 
  also 
  well 
  shown 
  by 
  the 
  iodides 
  of 
  the 
  

   other 
  metals 
  of 
  the 
  alkaline 
  earths. 
  Thus 
  I 
  have 
  observed 
  

   a 
  negative 
  emission 
  of 
  about 
  tw 
  T 
  o 
  milliamperes 
  from 
  a 
  layer 
  

   * 
  Phil. 
  Mag, 
  vol. 
  xxv. 
  p. 
  735 
  (1913). 
  

  

  