﻿1875.] 
  

  

  On 
  Electrolytic 
  Conduction 
  in 
  Solids. 
  

  

  463 
  

  

  V. 
  " 
  Electrolytic 
  Conduction 
  in 
  Solids. 
  — 
  First 
  Example. 
  Hot 
  

   Glass/' 
  By 
  Prof. 
  Sir 
  William 
  Thomson, 
  F.R.S. 
  Received 
  

   June 
  10, 
  1875. 
  

  

  Many 
  years 
  ago 
  I 
  projected 
  an 
  experiment 
  to 
  test 
  the 
  voltaic 
  relations 
  

   between 
  different 
  metals 
  with 
  glass 
  substituted 
  for 
  the 
  electrolytic 
  liquid 
  

   of 
  an 
  ordinary 
  simple 
  voltaic 
  cell, 
  and 
  with 
  so 
  high 
  a 
  temperature 
  that 
  

   the 
  glass 
  would 
  have 
  conducting-power 
  sufficient 
  to 
  allow 
  induction 
  

   through 
  it 
  to 
  rule 
  the 
  difference 
  of 
  potentials 
  between 
  the 
  two 
  metals. 
  

   Imperfect 
  instrumental 
  arrangements, 
  and 
  want 
  of 
  knowledge 
  of 
  the 
  

   temperature 
  at 
  which 
  glass 
  would 
  have 
  sufficient 
  conductivity 
  to 
  give 
  

   satisfactory 
  results, 
  have 
  hitherto 
  prevented 
  me 
  from 
  carrying 
  out 
  the 
  

   proposed 
  investigation. 
  The 
  quadrant 
  electrometer 
  has 
  supplied 
  the 
  first 
  

   of 
  these 
  deficiencies, 
  and 
  Mr. 
  Perry's 
  recent 
  experiments* 
  on 
  the 
  con- 
  

   ductivity 
  of 
  glass 
  at 
  different 
  temperatures 
  the 
  second. 
  The 
  investiga- 
  

   tion 
  has 
  now 
  been 
  resumed 
  ; 
  and 
  in 
  a 
  preliminary 
  experiment 
  I 
  have 
  

   already 
  obtained 
  a 
  very 
  decided 
  result. 
  

  

  The 
  drawing 
  shows 
  the 
  arrangement 
  adopted. 
  MN 
  is 
  a 
  brass 
  case 
  

   immersed 
  in 
  an 
  oil-bath. 
  A 
  copper 
  plate, 
  C, 
  of 
  5 
  centims. 
  diameter, 
  

   lies 
  in 
  the 
  case 
  on 
  a 
  block 
  of 
  wood 
  ; 
  it 
  is 
  kept 
  metallically 
  connected 
  with 
  

   the 
  outside 
  case, 
  E, 
  of 
  the 
  electrometer. 
  A 
  flint-glass 
  plate, 
  Gr, 
  which 
  is 
  

  

  found 
  to 
  insulate 
  very 
  well 
  at 
  ordinary 
  temperatures, 
  is 
  laid 
  upon 
  C. 
  A 
  

   zinc 
  plate, 
  Z, 
  lies 
  on 
  the 
  glass, 
  and 
  is 
  connected 
  with 
  the 
  insulated 
  elec- 
  

   trode, 
  I, 
  of 
  the 
  electrometer, 
  by 
  means 
  of 
  a 
  wire 
  attached 
  to 
  the 
  end 
  of 
  

   a 
  stout 
  metallic 
  stem, 
  A 
  Z, 
  passing 
  through 
  the 
  centre 
  of 
  an 
  open 
  vertical 
  

   tube 
  reaching 
  above 
  the 
  level 
  of 
  the 
  oil. 
  The 
  glass 
  was 
  heated 
  gradually, 
  

   and 
  was 
  usually 
  kept 
  between 
  100° 
  and 
  120° 
  C, 
  the 
  temperature 
  being 
  

   measured 
  by 
  a 
  thermometer, 
  B. 
  

  

  Even 
  below 
  50° 
  C. 
  there 
  is 
  a 
  decided 
  result, 
  but 
  shown 
  less 
  rapidly 
  

   * 
  See 
  infra, 
  p. 
  468. 
  

   VOL. 
  XXIII. 
  2 
  o 
  

  

  