﻿34 
  Prof. 
  Chattock 
  and 
  Mr. 
  Tyndall 
  on 
  Changes 
  

  

  On 
  taking 
  out 
  the 
  point 
  at 
  the 
  end 
  o£ 
  the 
  above 
  we 
  found 
  

   it 
  coated 
  with 
  a 
  light 
  buff 
  coloured 
  deposit 
  for 
  about 
  a 
  

   millimetre 
  up 
  its 
  sides, 
  which 
  disappeared 
  on 
  heating 
  to 
  

   redness. 
  

  

  When 
  a 
  foreign 
  gas 
  like 
  oxygen 
  is 
  present 
  in 
  any 
  quantity 
  

   in 
  hydrogen, 
  there 
  is 
  a 
  chance 
  of 
  an 
  appreciable 
  amount 
  of 
  it 
  

   being 
  ionized 
  at 
  the 
  discharging 
  point 
  along 
  with 
  the 
  hydrogen 
  

   itself. 
  This 
  may 
  well 
  complicate 
  the 
  chemical 
  processes 
  

   accompanying 
  discharge, 
  since 
  not 
  only 
  may 
  the 
  hydrogen 
  

   ions 
  promote 
  direct 
  combination 
  of 
  hydrogen 
  with 
  oxygen, 
  

   but 
  the 
  oxygen 
  ions 
  may 
  also 
  be 
  responsible 
  for 
  a 
  similar 
  but 
  

   independent 
  action 
  in 
  a 
  possibly 
  different 
  manner, 
  to 
  say 
  

   nothing 
  of 
  the 
  formation 
  of 
  ozone. 
  

  

  For 
  this 
  reason 
  the 
  most 
  interesting, 
  because 
  the 
  simplest 
  

   case 
  to 
  consider, 
  is 
  that 
  in 
  which 
  only 
  a 
  very 
  small 
  percentage 
  

   of 
  oxygen 
  is 
  present, 
  and 
  this 
  is 
  the 
  case 
  we 
  have 
  chiefly 
  

   studied. 
  

  

  When 
  the 
  amount 
  of 
  oxygen 
  present 
  is 
  small 
  — 
  say 
  under 
  

   0*01 
  per 
  cent. 
  — 
  it 
  is 
  possible 
  at 
  a 
  single 
  sitting 
  by 
  repeated 
  

   discharges 
  to 
  reach 
  a 
  point 
  where 
  further 
  discharges 
  produce 
  

   only 
  the 
  small 
  residual 
  contractions 
  observed 
  in 
  " 
  pure 
  '* 
  

   hydrogen. 
  This 
  point 
  is 
  a 
  very 
  definite 
  one. 
  For 
  some 
  time 
  

   before 
  it 
  is 
  reached, 
  the 
  contraction 
  per 
  coulomb 
  is 
  nearly 
  

   constant, 
  but 
  the 
  drop 
  to 
  the 
  smaller 
  value 
  occurs 
  quite 
  

   suddenly 
  when 
  it 
  comes. 
  We 
  have 
  determined 
  the 
  position 
  

   of 
  this 
  drop 
  for 
  small 
  percentages 
  of 
  both 
  air 
  and 
  oxygen 
  in 
  

   hydrogen, 
  with 
  both 
  positive 
  and 
  negative 
  discharge. 
  In 
  all 
  

   cases, 
  the 
  same 
  character 
  of 
  curve 
  was 
  obtained 
  on 
  plotting 
  

   the 
  contraction 
  per 
  coulomb 
  with 
  the 
  coulombs 
  discharged. 
  

   The 
  nearly 
  level 
  top 
  and 
  the 
  sudden 
  drop 
  were 
  always 
  marked 
  

   features 
  ; 
  the 
  curves 
  for 
  air 
  and 
  for 
  oxygen 
  were 
  practically 
  

   indistinguishable, 
  and 
  except 
  for 
  the 
  fact 
  that 
  negative 
  

   discharge 
  promotes 
  combination 
  more 
  rapidly 
  than 
  positive, 
  

   the 
  same 
  applies 
  to 
  the 
  curves 
  for 
  the 
  two 
  signs 
  of 
  current. 
  

   In 
  illustration 
  we 
  give 
  in 
  Curves 
  V. 
  the 
  results 
  for 
  negative 
  

   discharge 
  in 
  air. 
  The 
  curves 
  were 
  constructed 
  as 
  follows 
  — 
  

   the 
  axis 
  o£ 
  abscissae 
  was 
  divided 
  up 
  into 
  a 
  series 
  of 
  spans 
  

   representing 
  the 
  times 
  in 
  minutes 
  the 
  current 
  (1*08 
  micro- 
  

   am]).) 
  was 
  passed 
  in 
  successive 
  discharges, 
  and 
  at 
  the 
  centre 
  

   of 
  each 
  span 
  was 
  erected 
  an 
  ordinate 
  giving 
  the 
  change 
  of 
  

   pressure 
  produced 
  by 
  1*08 
  micro-ampere 
  flowing 
  for 
  one 
  

   minute. 
  The 
  area 
  of 
  t\w 
  figure 
  thus 
  gives 
  the 
  total 
  change 
  

   of 
  pressure 
  which 
  occurs 
  before 
  the 
  drop 
  is 
  reached. 
  It 
  will 
  

   be 
  noticed 
  that 
  the 
  curves 
  are 
  not 
  always 
  the 
  best 
  which 
  could 
  

   be 
  swept 
  through 
  the 
  experimental 
  points. 
  The 
  curves 
  

   drawn 
  were 
  as 
  a 
  matter 
  of 
  fact 
  obtained 
  as 
  explained 
  on 
  

  

  