﻿[ 
  607 
  ] 
  

  

  LXIX. 
  The 
  Absorption, 
  Dispersion, 
  and 
  Surface- 
  Col 
  our 
  of 
  

   Selenium. 
  By 
  K. 
  W. 
  Wood, 
  Professor 
  of 
  Experimental 
  

   Physics 
  in 
  tlie 
  Johns 
  Hopkins 
  University*. 
  

  

  THE 
  dispersion 
  curves 
  of 
  substances 
  with 
  absorption- 
  

   bands 
  lying 
  wholly 
  within 
  the 
  visible 
  or 
  infra-red 
  spec- 
  

   trum 
  have 
  been 
  carefully 
  examined 
  within 
  the 
  past 
  few 
  years, 
  

   in 
  connexion 
  with 
  the 
  modern 
  theory 
  of 
  dispersion. 
  To 
  the 
  

   best 
  of 
  my 
  knowledge 
  little 
  or 
  nothing 
  has 
  been 
  done 
  with 
  

   substances 
  in 
  which 
  the 
  absorption 
  begins 
  in 
  the 
  visible 
  spec- 
  

   trum 
  and 
  extends 
  into 
  the 
  remote 
  ultra-violet. 
  Of 
  these 
  

   media 
  amorphous 
  selenium 
  is 
  a 
  type, 
  strong 
  absorption 
  

   beginning 
  not 
  far 
  from 
  the 
  D 
  lines, 
  and 
  increasing 
  con- 
  

   tinuously 
  with 
  decreasing 
  wave-length 
  until, 
  in 
  the 
  ultra- 
  

   violet, 
  the 
  extinction 
  coefficient 
  has 
  as 
  high 
  a 
  value 
  as 
  in 
  the 
  

   case 
  of 
  metals. 
  Another 
  substance 
  which 
  I 
  have 
  found 
  

   worthy 
  of 
  investigation 
  is 
  nitroso-dimethyl-aniline. 
  This 
  

   substance 
  is 
  most 
  remarkable 
  in 
  its 
  behaviour. 
  It 
  crystallizes 
  

   in 
  green 
  lamina? 
  which 
  melt 
  at 
  85 
  degrees 
  and 
  can 
  be 
  formed 
  

   into 
  fluid 
  prisms 
  between 
  glass 
  plates. 
  These 
  prisms 
  must 
  

   be 
  kept 
  fluid 
  by 
  an 
  air-bath, 
  as 
  on 
  solidification 
  they 
  become 
  

   opaque. 
  A 
  prism 
  of 
  four 
  or 
  five 
  degrees 
  gives 
  a 
  most 
  

   astonishing 
  dispersion 
  when 
  an 
  incandescent 
  lamp 
  is 
  viewed 
  

   through 
  it. 
  It 
  is 
  quite 
  transparent 
  up 
  to 
  the 
  greenish-blue, 
  

   and 
  gives 
  a 
  spectrum 
  twelve 
  times 
  as 
  long 
  as 
  a 
  quartz 
  prism 
  

   of 
  equal 
  angle. 
  Pressed 
  into 
  a 
  thin 
  film, 
  it 
  seems 
  to 
  be 
  nearly 
  

   as 
  transparent 
  as 
  glass 
  of 
  a 
  very 
  pale 
  canary-yellow 
  colour 
  ; 
  

   but 
  if 
  the 
  transmitted 
  light 
  be 
  examined 
  with 
  a 
  spectroscope, 
  

   the 
  blue 
  and 
  violet 
  end 
  of 
  the 
  spectrum 
  is 
  cut 
  off 
  almost 
  as 
  

   sharply 
  as 
  if 
  by 
  an 
  opaque 
  screen 
  in 
  the 
  eyepiece. 
  This 
  

   indicates 
  an 
  exceedingly 
  steep 
  extinction 
  curve; 
  and 
  the 
  

   course 
  of 
  the 
  dispersion 
  curve 
  within 
  this 
  region 
  will 
  prove 
  

   most 
  interesting. 
  I 
  am 
  at 
  the 
  present 
  time 
  engaged 
  on 
  the 
  

   investigation 
  of 
  the 
  absorption 
  and 
  dispersion 
  of 
  this 
  sub- 
  

   stance, 
  and 
  further 
  discussion 
  will 
  be 
  postponed 
  for 
  the 
  

   present. 
  

  

  Selenium 
  I 
  have 
  already 
  investigated 
  with 
  the 
  assistance 
  of 
  

   Mr. 
  A. 
  H. 
  Pfund, 
  one 
  of 
  my 
  students 
  at 
  the 
  University 
  of 
  

   Wisconsin, 
  to 
  whom 
  I 
  am 
  indebted 
  for 
  a 
  large 
  amount 
  of 
  very 
  

   faithful 
  work. 
  

  

  The 
  only 
  determinations 
  that 
  I 
  have 
  been 
  able 
  to 
  find 
  of 
  

   the 
  dispersion 
  of 
  this 
  substance 
  were 
  made 
  by 
  Sirksf 
  by 
  the 
  

   method 
  of 
  the 
  colours 
  of 
  thin 
  plates 
  ; 
  a 
  method 
  involving 
  con- 
  

   siderable 
  error, 
  as 
  is 
  apparent 
  from 
  a 
  comparison 
  of 
  his 
  curve 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  February 
  28, 
  1902. 
  

   t 
  Sirks, 
  Dispersion 
  des 
  Selens, 
  Pog'g\ 
  Ann. 
  cxliii. 
  p. 
  429. 
  

  

  282 
  

  

  