﻿1875.] 
  on 
  the 
  Absorption- 
  Spectra 
  of 
  Metals. 
  345 
  

  

  lateral 
  orifices 
  were 
  cut 
  in 
  the 
  lime 
  for 
  the 
  insertion 
  of 
  tobacco-pipe 
  

   stems, 
  through 
  which 
  a 
  stream 
  of 
  hydrogen 
  could 
  be 
  passed 
  into 
  the 
  tube 
  

   and 
  receptacle. 
  

  

  An 
  electric 
  lamp 
  (F), 
  in 
  connexion 
  with 
  a 
  30-cell 
  Bunsen's 
  battery, 
  

  

  was 
  placed 
  opposite 
  one 
  end 
  of 
  the 
  tube, 
  and 
  a 
  spectroscope 
  (Gr) 
  opposite 
  

   the 
  other. 
  This 
  last 
  instrument 
  was 
  by 
  Desaga, 
  of 
  Heidelberg, 
  and 
  its 
  

   single 
  prism, 
  the 
  angle 
  of 
  which 
  was 
  60°, 
  was 
  capable 
  of 
  distinctly 
  sepa- 
  

   rating 
  the 
  D 
  lines, 
  at 
  the 
  same 
  time 
  that 
  it 
  enabled 
  us 
  to 
  see 
  the 
  whole 
  

   spectrum 
  in 
  a 
  siugle 
  field 
  of 
  view, 
  an 
  essential 
  point 
  in 
  such 
  inquiries. 
  

   The 
  magnifying-power 
  of 
  the 
  telescope 
  was 
  7*5 
  linear. 
  

  

  Some 
  preliminary 
  experiments 
  indicated 
  the 
  advisability 
  of 
  increasing 
  

   the 
  length 
  of 
  the 
  column 
  of 
  vapour. 
  To 
  effect 
  this, 
  a 
  tube 
  30 
  centims. 
  

   long 
  was 
  made 
  in 
  a 
  fresh 
  block 
  of 
  lime, 
  the 
  cavity 
  being 
  arranged 
  as 
  

   before 
  ; 
  in 
  each 
  end 
  a 
  short 
  accurately 
  fitting 
  iron 
  tube, 
  luted 
  with 
  a 
  

   mixture 
  of 
  graphite 
  and 
  fireclay, 
  was 
  inserted 
  ; 
  and 
  the 
  total 
  length 
  of 
  

   the 
  column 
  thus 
  became 
  60 
  centims. 
  

  

  The 
  lime 
  block 
  (C) 
  with 
  its 
  fittings 
  was 
  then 
  placed 
  in 
  the 
  charcoal- 
  

   furnace 
  (E), 
  by 
  means 
  of 
  which 
  the 
  whole 
  could 
  be 
  raised 
  to 
  a 
  high 
  tem- 
  

   perature. 
  As 
  soon 
  as 
  the 
  block 
  was 
  heated 
  to 
  bright 
  redness, 
  the 
  metal, 
  

   the 
  vapour 
  of 
  which 
  was 
  to 
  be 
  examined, 
  was 
  introduced 
  into 
  the 
  cavity 
  

   (C), 
  and 
  the 
  flame 
  of 
  the 
  oxyhydrogen 
  blowpipe 
  (D) 
  was 
  allowed 
  to 
  play 
  

   on 
  its 
  upper 
  surface, 
  care 
  being 
  taken 
  to 
  employ 
  an 
  excess 
  of 
  hydrogen. 
  

   In 
  almost 
  every 
  case 
  the 
  metal 
  experimented 
  on 
  was 
  rapidly 
  volatilized 
  

   (the 
  exceptions 
  being 
  gold 
  and 
  palladium). 
  The 
  central 
  portion 
  of 
  the 
  

  

  VOL. 
  XXIII. 
  2 
  D 
  

  

  