﻿882 
  Mr. 
  E. 
  Parr 
  Metcalfe 
  on 
  

  

  The 
  relative 
  molecular 
  ionization 
  in 
  the 
  gas 
  is 
  given 
  by 
  

  

  / 
  Current 
  in 
  gas 
  ^ 
  Current 
  in 
  air 
  \ 
  

   \ 
  Pressure 
  of 
  oas 
  ~ 
  Pressure 
  in 
  air/ 
  

  

  gas 
  

  

  1 
  ... 
  Pa-T. 
  

  

  or 
  

  

  PT 
  • 
  PT 
  PT 
  

  

  where 
  P^, 
  P^ 
  are 
  the 
  pressures 
  in 
  gas 
  and 
  air 
  respectively, 
  

   corrected 
  for 
  temperature 
  if 
  necessary, 
  and 
  T^, 
  %i 
  represent 
  

   the 
  times 
  taken 
  for 
  the 
  electrometer-needle 
  to 
  swing 
  through 
  

   the 
  range 
  corresponding 
  to 
  the 
  E.M.F. 
  of 
  a 
  Clark 
  cell. 
  At 
  

   the 
  comparatively 
  low 
  pressures 
  used 
  it 
  was 
  unnecessary 
  to 
  

   allow 
  for 
  deviations 
  from 
  Boyle's 
  law 
  or 
  for 
  change 
  in 
  the 
  

   capacity 
  of 
  the 
  electrode. 
  

  

  In 
  introducing 
  the 
  gas 
  into 
  the 
  chamber 
  the 
  precaution 
  

   was 
  taken 
  of 
  adjusting 
  its 
  pressure 
  so 
  that 
  its 
  stopping 
  power 
  

   for 
  a-radiation 
  should 
  be 
  approximately 
  the 
  same 
  as 
  that 
  of 
  

   the 
  air 
  previously 
  occupying 
  it. 
  The 
  stopping 
  power 
  is 
  calcu- 
  

   lated 
  as 
  being 
  proportional 
  to 
  the 
  sum 
  of 
  the 
  square 
  roots 
  of 
  

   the 
  weights 
  of 
  the 
  atoms 
  composing 
  the 
  molecule 
  of 
  the 
  gas 
  

   (Kleeman). 
  This 
  precaution 
  is 
  well 
  worth 
  taking 
  in 
  view 
  of 
  

   the 
  va^-iation 
  of 
  the 
  ionizing 
  power 
  of 
  the 
  a-particle 
  at 
  

   different 
  parts 
  of 
  its 
  range. 
  

  

  Hydrogen. 
  — 
  The 
  gas 
  was 
  prepared 
  by 
  the 
  slow 
  electrolysis 
  

   of 
  pure 
  dilute 
  H2SO4. 
  It 
  was 
  collected 
  over 
  the 
  electrolyte 
  

   and 
  allowed 
  to 
  stand 
  for 
  some 
  hours, 
  being 
  then 
  passed 
  in 
  a 
  

   slow 
  stream 
  through 
  a 
  train 
  of 
  purifiers 
  containing 
  succes- 
  

   sively 
  moist 
  caustic 
  potash 
  and 
  strong 
  H2SO4 
  : 
  it 
  was 
  stored 
  

   until 
  needed 
  (next 
  day) 
  over 
  phosphorus 
  pentoxide. 
  Two 
  

   sets 
  of 
  measurements 
  were 
  made, 
  the 
  sulphuric 
  acid 
  mano- 
  

   meter 
  being 
  used 
  for 
  both. 
  In 
  these 
  earlier 
  experiments 
  the 
  

   closed 
  limb 
  of 
  the 
  manometer 
  had 
  been 
  evacuated 
  and 
  sealed 
  

   off 
  from 
  the 
  pump. 
  It 
  was 
  found 
  that 
  after 
  three 
  or 
  four 
  

   days 
  a 
  small 
  quantity 
  of 
  dissolved 
  gas 
  was 
  liberated 
  from 
  the 
  

   112804, 
  and 
  that 
  its 
  pressure 
  became 
  sufficiently 
  great 
  to 
  

   necessitate 
  the 
  application 
  of 
  a 
  correction 
  to 
  the 
  manometer 
  

   indications. 
  For 
  this 
  reason 
  the 
  mercury 
  manometer 
  was 
  

   reverted 
  to 
  for 
  the 
  next 
  gas 
  (CO) 
  ; 
  but 
  it 
  was 
  so 
  unsatisfactory 
  

   that 
  an 
  arrangement 
  was 
  made 
  by 
  which 
  the 
  turning 
  of 
  a 
  

   double 
  tap 
  placed 
  the 
  closed 
  limb 
  of 
  the 
  manometer 
  in 
  com- 
  

   munication 
  either 
  with 
  the 
  other 
  limb, 
  or 
  with 
  the 
  pump, 
  or 
  

   isolated 
  it 
  altogether. 
  In 
  this 
  way 
  it 
  was 
  possible 
  to 
  remove 
  

   any 
  evolved 
  gas 
  which 
  might 
  have 
  collected 
  in 
  the 
  space 
  above 
  

   the 
  liquid 
  before 
  each 
  experiment. 
  The 
  results 
  obtained 
  for 
  

   hydrogen 
  are 
  in 
  very 
  close 
  agreement 
  : 
  they 
  are 
  also 
  not 
  far 
  

   from 
  the 
  two 
  values 
  given 
  by 
  Strutt 
  ('213 
  and 
  '226) 
  and 
  that 
  

   of 
  Bragg 
  (-24). 
  

  

  