﻿242 
  Scientific 
  Intelligence. 
  

  

  ments 
  have 
  been 
  made 
  by 
  Collie 
  and 
  Ramsay 
  to 
  determine: 
  

   1st, 
  the 
  distance 
  through 
  which 
  the 
  electric 
  spark 
  will 
  strike 
  

   through 
  argon 
  and 
  through 
  helium 
  at 
  atmospheric 
  pressure 
  ; 
  and 
  

   2d, 
  the 
  pressure 
  under 
  which 
  the 
  spark 
  discharge 
  changes 
  into 
  a 
  

   ribbon-like 
  discharge 
  in 
  these 
  gases, 
  as 
  compared 
  with 
  others. 
  

   Even 
  with 
  argon 
  it 
  was 
  found 
  that 
  the 
  length 
  of 
  the 
  spark 
  was 
  

   considerably 
  greater 
  than 
  with 
  air, 
  oxygen 
  or 
  hydrogen 
  ; 
  while 
  

   with 
  helium 
  the 
  distance 
  through 
  which 
  the 
  spark 
  would 
  pass 
  was 
  

   remarkable. 
  Thus 
  while 
  in 
  oxygen 
  the 
  spark-length 
  was 
  23*0 
  mm 
  , 
  

   in 
  air 
  33-0 
  mm 
  and 
  in 
  hydrogen 
  39'0 
  mm 
  , 
  in 
  argon 
  it 
  was 
  45'5 
  mm 
  and 
  

   in 
  helium 
  probably 
  250-300 
  mm 
  . 
  In 
  helium 
  the 
  discharge 
  was 
  a 
  

   blue 
  ribbon 
  of 
  flame 
  not 
  showing 
  the 
  D 
  3 
  line 
  very 
  distinctly. 
  

   Moreover 
  these 
  experiments 
  showed 
  that 
  the 
  spark 
  discharge 
  

   changed 
  to 
  the 
  ribbon 
  discharge 
  at 
  some 
  definite 
  pressure 
  in 
  all 
  

   gases. 
  Thus 
  in 
  air 
  it 
  occurred 
  at 
  73 
  or 
  74 
  mm 
  ; 
  in 
  hydrogen 
  at 
  42 
  

   or 
  43 
  mm 
  ; 
  in 
  oxygen 
  at 
  81 
  mm 
  ; 
  in 
  carbon 
  dioxide 
  at 
  92 
  or 
  94 
  mm 
  ; 
  in 
  

   cyanogen 
  at 
  23 
  mm 
  ; 
  in 
  nitrogen 
  at 
  33 
  mm 
  ; 
  in 
  carbon 
  monoxide 
  at 
  

   49 
  mm 
  ; 
  and 
  in 
  helium 
  at 
  1270 
  mm 
  . 
  Hence 
  helium 
  is 
  different 
  from 
  all 
  

   other 
  gases 
  in 
  this 
  respect. 
  So 
  that 
  a 
  Pliicker 
  tube 
  filled 
  with 
  

   helium 
  at 
  atmospheric 
  pressure 
  exhibits 
  all 
  the 
  phenomena 
  of 
  a 
  

   vacuum 
  tube. 
  

  

  In 
  a 
  second 
  series 
  of 
  experiments, 
  made 
  in 
  electrodeless 
  tubes, 
  

   at 
  different 
  pressures, 
  the 
  object 
  was 
  to 
  determine 
  the 
  quantity 
  of 
  

   one 
  gas 
  detectible 
  in 
  a 
  mixture 
  with 
  another, 
  and 
  thus 
  to 
  form 
  a 
  

   judgment 
  as 
  to 
  the 
  adequacy 
  of 
  the 
  spectrum 
  test 
  as 
  an 
  evidence 
  

   of 
  purity. 
  In 
  hydrogen 
  it 
  was 
  found 
  that 
  at 
  2 
  # 
  61 
  mm 
  33 
  per 
  cent 
  

   of 
  helium 
  was 
  quite 
  invisible, 
  while 
  at 
  the 
  lowest 
  pressures 
  10 
  

   per 
  cent 
  was 
  barely 
  visible. 
  Conversely 
  0*001 
  per 
  cent 
  of 
  hydro- 
  

   gen 
  is 
  visible 
  in 
  helium 
  at 
  all 
  pressures. 
  Nitrogen 
  0*01 
  per 
  cent 
  

   is 
  almost 
  invisible 
  in 
  helium; 
  while 
  10 
  per 
  cent 
  of 
  helium 
  in 
  

   nitrogen 
  can 
  be 
  detected 
  only 
  with 
  difficulty. 
  Argon 
  0*06 
  per 
  

   cent 
  can 
  be 
  detected 
  in 
  helium 
  at 
  all 
  pressures 
  ; 
  while 
  33 
  per 
  cent 
  

   of 
  helium 
  is 
  invisible 
  in 
  argon 
  at 
  2*62 
  mm 
  pressure 
  and 
  25 
  per 
  cent 
  

   is 
  invisible 
  at 
  0*58 
  mm 
  . 
  Nitrogen 
  0*42 
  per 
  cent 
  is 
  invisible 
  in 
  argon 
  

   at 
  0'l7 
  mm 
  pressure 
  and 
  0*08 
  per 
  cent 
  is 
  invisible 
  at 
  0'18 
  mm 
  , 
  

   although 
  just 
  visible 
  at 
  l*05 
  mm 
  . 
  Argon 
  37 
  per 
  cent 
  in 
  nitrogen 
  

   is 
  barely 
  visible 
  at 
  any 
  pressure 
  ; 
  while 
  in 
  oxygen 
  2 
  "3 
  per 
  cent 
  

   can 
  be 
  distinguished 
  only 
  with 
  difficulty 
  at 
  l*04 
  mm 
  . 
  The 
  lumi- 
  

   nosity 
  of 
  the 
  argon 
  spectrum 
  is 
  greatly 
  decreased 
  by 
  oxygen, 
  the 
  

   reduction 
  of 
  pressure 
  having 
  no 
  effect 
  in 
  intensifying 
  it. 
  — 
  Proc. 
  

   Boy. 
  Soc, 
  lix, 
  257, 
  1896. 
  g. 
  e. 
  b. 
  

  

  4. 
  On 
  the 
  Gases 
  obtained 
  from 
  Uraninite 
  and 
  Eliasite. 
  — 
  

   Observations 
  by 
  Lockyer 
  show 
  that 
  the 
  gases 
  obtained 
  from 
  

   the 
  mineral 
  eliasite 
  when 
  heated 
  in 
  a 
  vacuum 
  yield 
  spectra 
  con- 
  

   taining 
  the 
  lines 
  of 
  unknown 
  elements 
  as 
  well 
  as 
  of 
  known 
  ones, 
  

   many 
  of 
  these 
  being 
  probably 
  coincident 
  with 
  stellar 
  and 
  solar 
  

   lines, 
  although 
  in 
  somes 
  cases 
  no 
  coincidences 
  have 
  been 
  observed. 
  

   He 
  observes 
  that 
  the 
  composition 
  of 
  the 
  gas 
  varies 
  with 
  the 
  stage 
  

   of 
  the 
  heating 
  process, 
  no 
  trace 
  of 
  D 
  3 
  being 
  seen 
  in 
  the 
  first 
  two 
  

   portions 
  taken, 
  while 
  in 
  the 
  third 
  from 
  the 
  same 
  specimen 
  this 
  

  

  