﻿of 
  Pressure 
  which 
  accompany 
  Point 
  Discharge. 
  31 
  

  

  question 
  of 
  volumes 
  and 
  pressures. 
  The 
  pressure-gauges 
  

   AAA 
  were 
  for 
  measuring 
  the 
  latter. 
  

  

  Dummy 
  experiments 
  were 
  of 
  course 
  made 
  in 
  which 
  the 
  

   pure 
  hydrogen 
  was 
  pumped 
  over 
  and 
  back 
  before 
  impurity 
  

   was 
  put 
  into 
  M 
  ; 
  no 
  indication 
  that 
  the 
  hydrogen 
  had 
  been 
  

   contaminated 
  by 
  this 
  process 
  could 
  be 
  detected 
  when 
  all 
  was 
  

   working 
  properly. 
  

  

  The 
  usual 
  trouble 
  with 
  leaking 
  taps 
  was 
  experienced. 
  

   Mercury 
  seals 
  were 
  used 
  throughout 
  to 
  prevent 
  air 
  getting 
  

   in, 
  but 
  we 
  also 
  used 
  internal 
  mercury 
  seals 
  in 
  the 
  case 
  of 
  the 
  

   taps 
  marked 
  S. 
  The 
  plugs 
  of 
  these 
  taps 
  were 
  hollow 
  so 
  that 
  

   mercury 
  could 
  be 
  passed 
  into 
  them 
  from 
  outside 
  and 
  allowed 
  

   to 
  run 
  a 
  short 
  distance 
  along 
  the 
  connecting 
  tubes 
  while 
  the 
  

   plugs 
  were 
  open. 
  It 
  was 
  thus 
  impossible 
  for 
  gas 
  to 
  pass 
  the 
  

   plug 
  when 
  closed. 
  We 
  also 
  had 
  trouble 
  in 
  preventing 
  leakage 
  

   between 
  the 
  discharge 
  vessels 
  and 
  the 
  outer 
  air. 
  This 
  was 
  

   finally 
  overcome 
  by 
  completely 
  immersing 
  the 
  copper 
  casting 
  

   in 
  mercury. 
  

  

  Oxygen 
  in 
  Hydrogen. 
  

  

  The 
  large 
  permanent 
  contraction 
  that 
  occurs 
  when 
  oxygen 
  

   is 
  present 
  is 
  roughly 
  proportional 
  to 
  the 
  current 
  for 
  both 
  

   signs 
  of 
  discharge 
  from 
  about 
  2 
  to 
  9 
  micro-amperes. 
  This 
  is 
  

   shown 
  by 
  Curves 
  III., 
  which 
  were 
  taken 
  with 
  hydrogen 
  

   containing 
  between 
  1 
  and 
  2 
  per 
  cent, 
  of 
  oxygen. 
  

  

  With 
  smaller 
  currents 
  negative 
  discharge 
  gives 
  values 
  of 
  

   p 
  which 
  are 
  too 
  small. 
  At 
  1 
  microampere 
  for 
  instance 
  p 
  is 
  

   about 
  6*5 
  per 
  cent, 
  too 
  small 
  compared 
  with 
  its 
  value 
  for 
  

   twice 
  that 
  current. 
  Positive 
  discharge 
  does 
  not 
  show 
  this 
  

   discrepancy. 
  

  

  Similarly 
  p 
  is 
  proportional, 
  for 
  both 
  signs, 
  to 
  the 
  duration 
  

   of 
  the 
  current 
  from 
  about 
  half 
  a 
  minute's 
  interval 
  upwards. 
  

   Below 
  this 
  interval 
  the 
  time 
  required 
  to 
  start 
  the 
  current 
  

   introduces 
  too 
  much 
  error 
  for 
  a 
  test 
  to 
  be 
  possible. 
  

  

  The 
  values 
  given 
  in 
  Curves 
  III. 
  were 
  obtained 
  by 
  passing 
  

   the 
  various 
  currents 
  for 
  10 
  minute 
  intervals. 
  This 
  happened 
  

   to 
  give 
  time 
  for 
  the 
  temperature 
  of 
  the 
  gas 
  to 
  become 
  steady 
  

   during 
  the 
  last 
  four 
  or 
  five 
  minutes 
  of 
  the 
  discharge 
  ; 
  and 
  

   the 
  slope 
  of 
  the 
  pressure 
  curve 
  in 
  this 
  region, 
  when 
  corrected 
  

   for 
  drift 
  (S, 
  in 
  Curves 
  I 
  c) 
  , 
  was 
  therefore 
  due 
  to 
  the 
  formation 
  

   of 
  the 
  water- 
  vapour 
  only. 
  

  

  It 
  follows 
  that 
  p 
  should 
  be 
  calculable 
  from 
  this 
  slope 
  

   (say 
  pi) 
  as 
  well 
  as 
  from 
  the 
  pressures 
  before 
  and 
  after 
  dis- 
  

   charge 
  (/?). 
  In 
  Table 
  1 
  we 
  give 
  the 
  ratios 
  p/pi 
  calculated 
  

   from 
  the 
  data 
  of 
  Curves 
  III. 
  

  

  