﻿Water 
  Vapour 
  in 
  Gaseous 
  Conduction, 
  513 
  

  

  not 
  seem 
  material, 
  for 
  we 
  know 
  that 
  all 
  fairly 
  dry 
  dust-free 
  

   gases 
  are 
  insulators 
  under 
  ordinary 
  conditions. 
  It 
  is 
  still 
  to 
  

   be 
  shown 
  that 
  pure 
  hydrogen 
  under 
  electric 
  stress 
  in 
  a 
  vacuum- 
  

   tube 
  is 
  an 
  insulator.. 
  

  

  Another 
  reason 
  assigned 
  by 
  Professor 
  Trowbridge 
  for 
  

   holding 
  hydrogen 
  to 
  be 
  an 
  insulator, 
  is 
  that 
  when 
  occluded 
  by 
  

   platinum 
  or 
  palladium 
  the 
  resistance 
  of 
  these 
  metals 
  is 
  in- 
  

   creased. 
  It 
  must 
  be 
  remembered, 
  however, 
  that 
  alloys 
  usually 
  

   have' 
  a 
  greater 
  specific 
  resistance 
  than 
  that 
  of 
  either 
  of 
  their 
  

   constituents. 
  Silver 
  added 
  to 
  platinum 
  gives 
  an 
  alloy 
  with 
  

   more 
  than 
  twice 
  the 
  specific 
  resistance 
  of 
  platinum, 
  yet 
  no 
  

   one 
  can 
  claim 
  that 
  silver 
  is 
  an 
  insulator. 
  Nor 
  is 
  the 
  condition 
  

   of 
  hydrogen 
  when 
  occluded, 
  or 
  when, 
  liquefied, 
  the 
  same 
  as 
  

   that 
  in 
  vacuum-tubes. 
  

  

  In 
  the 
  second 
  place, 
  it 
  seems 
  that 
  the 
  complete 
  removal 
  of 
  

   water-vapour 
  from 
  vacuum-tubes 
  is 
  perhaps 
  possible, 
  and 
  that. 
  

   still 
  the 
  hydrogen 
  or 
  other 
  gases 
  contained 
  therein 
  may 
  

   transmit 
  the 
  current 
  and 
  give 
  their 
  characteristic 
  spectra. 
  

   All 
  who 
  have 
  worked 
  with 
  vacuum-tubes 
  know 
  how 
  pertina- 
  

   cious 
  water-vapour 
  is 
  ; 
  but 
  some 
  experiments 
  by 
  Deslandres 
  * 
  

   and 
  by 
  the 
  present 
  writer 
  f 
  indicate 
  that 
  it 
  may 
  be 
  effectively 
  

   removed 
  by 
  the 
  prolonged 
  heating 
  of 
  metallic 
  sodium 
  in 
  

   the 
  tube. 
  Deslandres 
  states 
  that 
  only 
  by 
  such 
  treatment 
  

   could 
  he 
  cause 
  the 
  characteristic 
  water-vapour 
  lines 
  to 
  dis- 
  

   appear 
  from 
  the 
  spectrum 
  of 
  nitrogen., 
  and 
  it 
  also 
  causes 
  the 
  

   disappearance 
  of 
  that 
  group 
  of 
  bands 
  in 
  the 
  extreme 
  ultra- 
  

   violet 
  spectrum 
  of 
  nitrogen 
  attributed 
  by 
  Deslandres 
  to 
  an 
  

   oxide 
  of 
  nitrogen, 
  while 
  the 
  remaining 
  part 
  of 
  the 
  nitrogen 
  

   spectrum 
  was 
  as 
  bright 
  as 
  or 
  brighter 
  than 
  before. 
  

  

  E. 
  Wiedemann 
  % 
  heated 
  metallic 
  sodium 
  in 
  vacuum-tubes 
  

   containing 
  hydrogen 
  or 
  nitrogen. 
  As 
  the 
  vapour-density 
  of 
  

   the 
  sodium 
  increased, 
  its 
  spectrum 
  grew 
  in 
  intensity 
  at 
  the 
  

   expense 
  of 
  that 
  of 
  the 
  other 
  gas 
  ; 
  but 
  on 
  cooling 
  the 
  tube, 
  

   the 
  hydrogen 
  or 
  nitrogen 
  spectrum 
  reassumed 
  its 
  original 
  

   appearance. 
  

  

  In 
  order 
  to 
  again 
  test 
  the 
  matter, 
  the 
  writer 
  recently 
  placed 
  

   a 
  quantity 
  of 
  metallic 
  sodium 
  in 
  a 
  vacuum-tube 
  containing 
  

   hydrogen. 
  The 
  sodium 
  was 
  repeatedly 
  heated 
  to 
  drive 
  off 
  its 
  

   more 
  volatile 
  impurities, 
  and 
  the 
  tube 
  pumped 
  out 
  and 
  filled 
  

   with 
  fresh 
  electrolytically 
  prepared 
  hydrogen. 
  After 
  the 
  tube 
  

   had 
  been 
  well 
  covered 
  with 
  sodium 
  " 
  dew," 
  it 
  was 
  closed.. 
  For 
  

   two 
  weeks 
  it 
  was 
  frequently 
  heated, 
  and 
  the 
  spectrum 
  ex- 
  

   amined 
  by 
  a 
  pocket 
  spectroscope. 
  After 
  heating, 
  or 
  in 
  parts 
  of 
  

  

  * 
  Deslandres, 
  Ann. 
  de 
  Chim. 
  et 
  de 
  Phys. 
  [6] 
  xv. 
  p. 
  46 
  (1888). 
  

   f 
  Lewis, 
  Ann. 
  der 
  Physik 
  [4] 
  ii. 
  p. 
  465 
  (1900). 
  

   X 
  E. 
  Wiedemann, 
  Wied. 
  Ann. 
  v. 
  p. 
  517 
  (1878). 
  

  

  