﻿202 
  Radioactivity 
  imparted 
  to 
  Salts 
  by 
  Cathode 
  Rays, 
  

  

  Table 
  II. 
  

  

  Solid 
  Solution. 
  

  

  Gold 
  leaf 
  

   positively 
  

   charged. 
  

  

  Gold 
  leaf 
  

   negatively 
  

   charged. 
  

  

  Thermo- 
  

   luminescence. 
  

  

  CaS0 
  4 
  +2 
  p.c. 
  MnS0 
  4 
  

   ZnS0 
  4 
  +lp.c.MnS0 
  4 
  

   MgS0 
  4 
  + 
  lp.c.MnS0 
  4 
  

   CdS0 
  4 
  -flp.c. 
  MnS0 
  4 
  

   CaFl 
  2 
  +2 
  p.c. 
  MnFl 
  2 
  

  

  Leak. 
  

   No 
  leak. 
  

  

  J) 
  55 
  

  

  No 
  leak. 
  

  

  )) 
  J) 
  

  

  Intense 
  green. 
  

   Intense 
  red. 
  

   Intense 
  dark 
  red. 
  

   Intense 
  yellow. 
  

   Bright 
  green. 
  

  

  Since, 
  therefore, 
  radioactivity 
  was 
  impressed 
  on 
  but 
  one 
  of 
  

   the 
  five 
  solid 
  solutions, 
  while 
  they 
  all 
  exhibited 
  a 
  very 
  

   powerful 
  thermoluminescence, 
  it 
  seems 
  obvious 
  that 
  no 
  direct 
  

   connexion 
  exists 
  between 
  the 
  two 
  phenomena. 
  

  

  This 
  conclusion 
  is 
  also 
  confirmed 
  by 
  the 
  fact 
  that 
  while 
  a 
  

   temperature 
  of 
  100° 
  G. 
  } 
  or 
  even 
  less, 
  sufficed 
  to 
  exhibit 
  

   radioactivity 
  in 
  connexion 
  with 
  most 
  of 
  the 
  salts 
  examined, 
  a 
  

   temperature 
  considerably 
  higher 
  than 
  this 
  was 
  found 
  to 
  be 
  

   necessary 
  to 
  produce 
  visible 
  thermoluminescence. 
  In 
  fact, 
  in 
  

   a 
  test 
  made 
  with 
  the 
  sulphates 
  of 
  strontium 
  and 
  barium 
  the 
  

   radioactivity 
  had 
  almost 
  entirely 
  disappeared 
  before 
  thermo- 
  

   luminescence 
  became 
  well-marked. 
  

  

  Moreover 
  a 
  difference 
  exists 
  in 
  the 
  intervals 
  of 
  time 
  during 
  

   which 
  the 
  excited 
  salts 
  retain 
  the 
  power 
  to 
  exhibit 
  the 
  two 
  

   phenomena. 
  As 
  is 
  well 
  known, 
  bodies 
  exhibiting 
  thermo- 
  

   luminescence 
  retain 
  this 
  property 
  for 
  weeks, 
  or 
  even 
  months, 
  

   after 
  exposure 
  to 
  cathode 
  rays. 
  On 
  the 
  other 
  hand, 
  the 
  

   present 
  investigation 
  goes 
  to 
  show 
  that 
  salts 
  rendered 
  radio- 
  

   active 
  by 
  cathode 
  rays 
  completely 
  lose 
  their 
  activitv 
  in 
  the 
  

   course 
  of 
  one 
  or, 
  at 
  most, 
  two 
  or 
  three 
  days. 
  

  

  VI. 
  diameter 
  of 
  the 
  Radiation. 
  

  

  An 
  experiment 
  was 
  made 
  to 
  see 
  whether 
  the 
  radioactivity 
  

   could 
  be 
  detected 
  when 
  the 
  electrostatic 
  field 
  of 
  the 
  gold 
  leaf 
  

   was 
  screened 
  oft' 
  from 
  the 
  salt 
  by 
  means 
  of 
  a 
  sheet 
  of 
  wire 
  

   gauze 
  placed 
  above 
  the 
  salt, 
  as 
  shown 
  by 
  the 
  dotted 
  line 
  

   in 
  fig. 
  1. 
  Little 
  difference 
  was 
  observed 
  when 
  gauze 
  with 
  

   meshes 
  3 
  millimetres 
  in 
  width 
  was 
  used, 
  but 
  with 
  gauze 
  

   made 
  from 
  wires 
  1 
  mm. 
  in 
  diameter, 
  placed 
  1 
  mm. 
  apart, 
  the 
  

   leak 
  from 
  the 
  measuring 
  system 
  was 
  greatly 
  diminished. 
  

  

  From 
  the 
  experiments 
  made 
  so 
  far, 
  there 
  appear 
  to 
  be 
  but 
  

  

  