﻿292 
  Dr. 
  H. 
  L. 
  Bronson 
  : 
  Relative 
  Activity 
  of 
  Emanation 
  

  

  for 
  a 
  very 
  small 
  correction, 
  was 
  a 
  measure 
  of 
  the 
  ionization 
  

   due 
  to 
  the 
  emanation. 
  I£ 
  the 
  active 
  deposit 
  had 
  not 
  reached 
  

   a 
  maximum, 
  it 
  was 
  easily 
  calculated, 
  since 
  the 
  rates 
  of 
  trans- 
  

   formation 
  of 
  all 
  the 
  products 
  involved 
  were 
  known. 
  

  

  All 
  the 
  measurements 
  were 
  made 
  by 
  means 
  of 
  an 
  electro- 
  

   meter 
  and 
  " 
  constant 
  deflexion 
  method/' 
  and 
  some 
  of 
  them 
  

   were 
  verified 
  by 
  means 
  of 
  the 
  " 
  rate 
  " 
  method 
  to 
  insure 
  that 
  

   no 
  serious 
  mistakes 
  were 
  being 
  made. 
  Two 
  cylindrical 
  

   testing 
  vessels 
  were 
  used. 
  Both 
  were 
  40 
  cms. 
  long, 
  and 
  had 
  

   central 
  electrodes 
  about 
  0'2 
  cm. 
  in 
  diameter. 
  The 
  diameters 
  

   of 
  the 
  testing 
  vessels 
  were 
  18 
  cms. 
  and 
  3' 
  6 
  cms. 
  respectively. 
  

   The 
  largest 
  one 
  allowed 
  the 
  a 
  particles 
  of 
  the 
  active 
  deposit 
  

   on 
  the 
  central 
  electrode 
  to 
  be 
  entirely 
  absorbed 
  in 
  the 
  air, 
  

   except 
  at 
  the 
  ends. 
  The 
  smaller 
  one 
  made 
  the 
  mean 
  free 
  

   path 
  of 
  the 
  a 
  particles 
  from 
  the 
  different 
  active 
  substances 
  

   more 
  nearly 
  equal. 
  

  

  All 
  the 
  experiments 
  were 
  repeated 
  several 
  times 
  under 
  as 
  

   different 
  conditions 
  as 
  possible. 
  The 
  quantity 
  of 
  thorium 
  

   and 
  actinium 
  used, 
  the 
  velocity 
  of 
  the 
  air 
  current, 
  and 
  the 
  

   saturation 
  potential 
  on 
  the 
  testing 
  vessel, 
  were 
  all 
  changed 
  

   several 
  times. 
  The 
  saturation 
  potential 
  was 
  changed 
  from 
  

   <30 
  to 
  600 
  volts, 
  and 
  both 
  positive 
  and 
  negative 
  values 
  were 
  

   used. 
  Thus 
  the 
  active 
  deposit 
  was 
  sometimes 
  deposited 
  on 
  

   the 
  central 
  electrode 
  and 
  sometimes 
  on 
  the 
  cylindrical 
  surface. 
  

   In 
  order 
  to 
  make 
  sure 
  of 
  this 
  point 
  for 
  the 
  sake 
  of 
  calculation, 
  

   the 
  central 
  electrode 
  was 
  removed 
  and 
  tested, 
  and 
  found 
  to 
  

   have 
  on 
  its 
  surface 
  more 
  than 
  90 
  per 
  cent, 
  of 
  the 
  active 
  

   deposit, 
  when 
  the 
  outside 
  of 
  the 
  testing 
  vessel 
  was 
  connected 
  

   to 
  the 
  positive 
  pole 
  of 
  the 
  battery. 
  A 
  second 
  testing 
  vessel 
  

   was 
  put 
  in 
  series 
  with 
  the 
  first 
  one, 
  to 
  make 
  sure 
  that 
  none 
  

   of 
  the 
  active 
  deposit 
  was 
  drawn 
  through 
  by 
  the 
  air 
  current. 
  

   No 
  evidence 
  of 
  this 
  was 
  ever 
  detected. 
  

  

  Measurements 
  and 
  Calculations. 
  

  

  Table 
  I. 
  gives 
  a 
  sample 
  set 
  of 
  observations 
  obtained 
  with 
  

   the 
  thorium 
  emanation 
  in 
  the 
  larger 
  testing 
  vessel. 
  

  

  The 
  time 
  was 
  reckoned 
  from 
  the 
  starting 
  of 
  the 
  emanation 
  

   through 
  the 
  testing 
  vessel. 
  The 
  maximum 
  value 
  of 
  the 
  active 
  

   deposit 
  was 
  calculated 
  on 
  the 
  assumption 
  that 
  thorium 
  A 
  

   decays 
  to 
  half 
  value 
  in 
  10*6 
  hours. 
  There 
  are 
  small 
  irregular 
  

   variations 
  in 
  the 
  ionization 
  currents, 
  which 
  are 
  due 
  to 
  slight 
  

   changes 
  in 
  the 
  velocity 
  of 
  the 
  air 
  current, 
  and 
  to 
  the 
  

   humidity, 
  which 
  affects 
  considerably 
  the 
  emanating 
  power 
  of 
  

   the 
  thorium. 
  

  

  At 
  the 
  end 
  of 
  88 
  hours 
  the 
  air 
  current 
  and 
  potential 
  of 
  

   the 
  testing 
  vessel 
  were 
  changed 
  and 
  another 
  set 
  of 
  measure- 
  

   ments 
  taken. 
  Several 
  such 
  changes 
  were 
  made, 
  and 
  the 
  

  

  