﻿858 
  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  are 
  given 
  in 
  fig. 
  13 
  (PI. 
  XXIY.). 
  The 
  rotatory 
  power 
  as 
  shown 
  

   in 
  the 
  table 
  is 
  more 
  than 
  double 
  that 
  obtained 
  bv 
  Lobach. 
  

  

  Table 
  XVI.— 
  Electrolytic 
  Cobalt. 
  

   Thickness. 
  31 
  x 
  10" 
  7 
  cm. 
  Field. 
  13,500 
  C.G.S. 
  

  

  Wave- 
  Rotation 
  

   length. 
  (deg.). 
  

  

  Ellipticity 
  

  

  X 
  13 
  ■•■. 
  

  

  Botat 
  5 
  

   Thick. 
  X 
  ' 
  

  

  Extinction 
  

  

  x 
  io- 
  5 
  . 
  

  

  440 
  

  

  480 
  

  

  600 
  

  

  520 
  

  

  540 
  

  

  560 
  

  

  580 
  

  

  600 
  

  

  620 
  

  

  680 
  

  

  »;io 
  

  

  ceo 
  

  

  •04 
  

   •99 
  

  

  i'o'o 
  

  

  1 
  10 
  

   119 
  

   i-22 
  

  

  i'-i'.V 
  

  

  9-6 
  

   9-5 
  

  

  8*9 
  ' 
  

  

  

  

  B-4 
  

  

  

  

  74 
  

   6-6 
  ' 
  

  

  V.'t" 
  

  

  303 
  

   819 
  

  

  323 
  

  

  3-55 
  

  

  3-84 
  

  

  394 
  

  

  i'os 
  

  

  90 
  

   90 
  

   91 
  

  

  9-0 
  

   8-9 
  

   90 
  

  

  8-9 
  

  

  8-7 
  

  

  8-8 
  

  

  8-9 
  

  

  The 
  extinction 
  (also 
  more 
  tlian 
  twice 
  that 
  given 
  by 
  Lobach) 
  

   was 
  obtained 
  in 
  the 
  same 
  manner 
  as 
  that 
  of 
  electrolytic 
  iron, 
  

   by 
  measuring 
  the 
  transmission 
  of 
  a 
  film 
  of 
  definite 
  thickness, 
  

   then 
  depositing 
  over 
  tlii> 
  and 
  repeating 
  the 
  measurements. 
  

   The 
  results 
  as 
  given 
  arc 
  the 
  mean 
  of 
  two 
  sets 
  obtained 
  from 
  

   different 
  films. 
  The 
  extinction 
  curve 
  (fig. 
  13) 
  is 
  flatter 
  than 
  

   thai 
  of 
  electrolytic 
  iron. 
  The 
  form 
  of 
  the 
  ellipticity 
  curve 
  

   appears 
  to 
  indicate 
  also 
  that 
  the 
  absorption 
  region 
  is 
  effec- 
  

   tively 
  farther 
  out 
  in 
  the 
  ultra-violet 
  than 
  that 
  of 
  the 
  iron. 
  

   The 
  difference 
  in 
  the 
  results 
  from 
  this 
  form 
  of 
  cobalt 
  and 
  

   the 
  dark 
  is 
  nearly 
  as 
  striking 
  as 
  that 
  between 
  the 
  corre- 
  

   sponding 
  types 
  of 
  iron. 
  

  

  14. 
  Metallic 
  Cobalt. 
  

  

  Films 
  of 
  cobalt 
  designated 
  as 
  metallic 
  were 
  readily 
  obtained 
  

   by 
  deposit 
  from 
  a 
  very 
  hot 
  cathode 
  with 
  a 
  glow 
  current 
  

   through 
  hydrogen. 
  Like 
  iron 
  they 
  are 
  brilliant 
  mirrors, 
  

   though 
  for 
  the 
  same 
  thickness 
  much 
  more 
  transparent. 
  Also 
  

   like 
  the 
  iron 
  they 
  impart 
  no 
  tint 
  to 
  transmitted 
  light. 
  

  

  In 
  figure 
  14 
  are 
  plotted 
  the 
  curves 
  of 
  rotation, 
  ellipticity, 
  

   transmission, 
  and 
  rotation 
  by 
  reflexion 
  of 
  a 
  representative 
  

   film. 
  Only 
  a 
  slight 
  trace 
  of 
  ellipticity 
  by 
  reflexion 
  was 
  

   observed. 
  The 
  forms 
  of 
  the 
  curves 
  are 
  very 
  similar 
  to 
  those 
  

   of 
  the 
  corresponding 
  type 
  of 
  iron 
  (fig. 
  8). 
  

  

  