﻿Experiments 
  ivith 
  the 
  Active 
  Deposit 
  of 
  Thorium. 
  359 
  

  

  stannous 
  chloride, 
  zinc 
  chloride, 
  or 
  even 
  ammonium 
  chloride 
  

   added, 
  and 
  the 
  solution 
  boiled 
  to 
  dryness 
  and 
  heated 
  as 
  

   before, 
  then 
  practically 
  the 
  whole 
  of 
  the 
  C 
  can 
  be 
  carried 
  off 
  

   by 
  the 
  fumes 
  of 
  the 
  added 
  salt. 
  It 
  would 
  appear 
  that 
  the 
  

   G 
  is 
  carried 
  off 
  by 
  some 
  sort 
  of 
  mechanical 
  action 
  rather 
  

   than 
  by 
  its 
  forming 
  compounds 
  of 
  increased 
  volatility. 
  In 
  

   these 
  experiments 
  the 
  temperatures 
  were 
  not 
  measured 
  

   accurately, 
  but 
  probably 
  the 
  highest 
  temperature 
  was 
  from 
  

   250° 
  C. 
  to 
  300° 
  C. 
  in 
  each 
  case. 
  

  

  It 
  appears 
  probable 
  that 
  in 
  Miss 
  Meitner's 
  experiment 
  

   with 
  stannous 
  chloride 
  the 
  nickel 
  plates 
  remove 
  only 
  about 
  

   80 
  per 
  cent, 
  of 
  the 
  C. 
  When 
  the 
  resulting 
  solution 
  is 
  heated 
  

   the 
  a-ray 
  portion, 
  which 
  consists 
  of 
  only 
  one 
  drop, 
  needs 
  

   very 
  little 
  heating 
  to 
  boil 
  it 
  to 
  dryness. 
  The 
  remainder, 
  

   however, 
  needs 
  much 
  more 
  heating, 
  due 
  to 
  its 
  larger 
  amount,, 
  

   and 
  as 
  volatilization 
  is 
  a 
  time-effect, 
  practically 
  the 
  whole 
  of 
  

   the 
  remaining 
  is 
  evaporated, 
  so 
  that 
  the 
  activity 
  rises 
  

   from 
  zero. 
  In 
  the 
  case 
  when 
  no 
  stannous 
  chloride 
  is 
  added, 
  

   however, 
  the 
  nickel 
  plates 
  are 
  more 
  efficient 
  in 
  removing 
  the 
  

   C, 
  due 
  to 
  there 
  being 
  no 
  impurity 
  present, 
  and, 
  moreover, 
  if 
  

   a 
  small 
  amount 
  of 
  is 
  left 
  it 
  is 
  not 
  so 
  volatile 
  as 
  when 
  

   stannous 
  chloride 
  is 
  present 
  to 
  carry 
  it 
  away. 
  

  

  We 
  made 
  observations 
  of 
  "rise 
  curves" 
  (see 
  fig. 
  1) 
  

   without 
  evaporating 
  the 
  7- 
  ray 
  portion 
  to 
  dryness, 
  and 
  found 
  

   ihat 
  the 
  a- 
  and 
  7-ray 
  activities 
  rose 
  proportionately. 
  Further 
  

   observations 
  were 
  made 
  of 
  the 
  rise 
  curves 
  by 
  a 
  rays, 
  (1) 
  with 
  

   the 
  source 
  uncovered, 
  and 
  (2) 
  with 
  the 
  source 
  covered 
  with 
  

   foils 
  sufficiently 
  thick 
  to 
  absorb 
  the 
  a 
  particles 
  of 
  short 
  range. 
  

   When 
  reduced 
  to 
  the 
  same 
  maximum 
  the 
  curves 
  showed 
  no 
  

   difference, 
  indicating 
  that 
  no 
  true 
  separation 
  of 
  the 
  products 
  

   emitting 
  the 
  two 
  sets 
  of 
  a 
  particles 
  had 
  taken 
  place. 
  In 
  

   another 
  experiment 
  a 
  hydrochloric 
  acid 
  solution 
  of 
  the 
  active 
  

   deposit 
  was 
  taken 
  and 
  divided 
  into 
  two 
  portions, 
  to 
  one 
  of 
  

   which 
  a 
  few 
  drops 
  of 
  stannous 
  chloride 
  were 
  added. 
  On 
  

   completely 
  evaporating 
  to 
  dryness 
  it 
  was 
  found 
  that 
  much 
  

   more 
  C 
  had 
  been 
  volatilized 
  in 
  the 
  latter 
  case 
  than 
  in 
  the 
  

   former. 
  

  

  In 
  consideration 
  of 
  Miss 
  Meitner's 
  "rise 
  curves 
  " 
  by 
  a 
  and 
  

   7 
  rays, 
  moreover 
  (fig. 
  1), 
  it 
  must 
  be 
  remembered 
  that 
  the 
  

   7 
  rays 
  are 
  emitted 
  by 
  D, 
  which 
  lags 
  behind 
  0, 
  the 
  origin 
  of 
  

   the 
  u 
  rays. 
  This 
  is 
  shown 
  by 
  the 
  theoretical 
  curves 
  for 
  C 
  

   and 
  D, 
  of 
  which 
  the 
  initial 
  parts 
  are 
  given 
  in 
  fig. 
  3, 
  the 
  scale 
  

   being 
  such 
  that 
  the 
  ordinates 
  are 
  percentages 
  of 
  the 
  maxi- 
  

   mum 
  activity 
  in 
  each 
  case. 
  It 
  will 
  be 
  seen 
  that 
  D 
  apparently 
  

   rises 
  from 
  6 
  per 
  cent, 
  below 
  C. 
  

  

  An 
  increased 
  initial 
  difference 
  between 
  the 
  curves 
  arises 
  

  

  