﻿Hobbs 
  — 
  Crystal 
  Form 
  of 
  Borneol 
  and 
  Isoborneol. 
  451 
  

  

  The 
  crystals 
  have 
  very 
  perfect 
  cleavage 
  parallel 
  to 
  the 
  base 
  

   and 
  the 
  rhombohedron 
  q. 
  They 
  are 
  very 
  flexible 
  and 
  care 
  

   must 
  be 
  used 
  in 
  handling 
  them 
  before 
  measurement. 
  Pittings 
  

   on 
  the 
  basal 
  pinacoid 
  are 
  trisym 
  metric 
  with 
  the 
  lines 
  of 
  sym- 
  

   metry 
  meeting 
  at 
  angles 
  of 
  120°. 
  

  

  Examined 
  under 
  the 
  polarizing 
  microscope 
  basal 
  sections 
  of 
  

   these 
  crystals 
  appear 
  isotropic 
  and 
  afford 
  no 
  interference 
  figure. 
  

   Sections 
  parallel 
  to 
  the 
  prism 
  exhibit 
  very 
  weak 
  double 
  refrac- 
  

   tion. 
  In 
  sections 
  2 
  mm 
  . 
  in 
  thickness 
  the 
  double 
  refraction 
  is 
  

   faintly 
  perceptible 
  without 
  the 
  use 
  of 
  a 
  quartz 
  plate. 
  In 
  sec- 
  

   tions 
  3 
  mm 
  . 
  in 
  thickness 
  the 
  double 
  refraction 
  is 
  easily 
  determined 
  

   with 
  use 
  of 
  the 
  quarter 
  undulation 
  mica 
  place. 
  A 
  consider- 
  

   able 
  number 
  of 
  sections 
  were 
  tested 
  and 
  all 
  were 
  found 
  to 
  be 
  

   negative. 
  In 
  these 
  sections 
  the 
  interference 
  color 
  only 
  reaches 
  

   the 
  yellow 
  of 
  the 
  first 
  order 
  when 
  the 
  corresponding 
  axes 
  of 
  

   the 
  crystal 
  and 
  the 
  mica 
  plate 
  are 
  parallel. 
  These 
  characters 
  

   therefore 
  agree 
  well 
  with 
  those 
  determined 
  for 
  this 
  substance 
  

   by 
  Traube. 
  The 
  borneol 
  prepared 
  from 
  Abies 
  balsamia 
  is 
  

   optically 
  identical 
  with 
  this. 
  

  

  Isoborneol 
  from 
  Turpentine. 
  As 
  already 
  stated, 
  the 
  sym- 
  

   metry 
  of 
  this 
  substance 
  is 
  the 
  same 
  as 
  that 
  of 
  borneol 
  and 
  the 
  

   axial 
  ratio 
  is 
  also 
  so 
  nearly 
  identical 
  that 
  the 
  measurements 
  af- 
  

   forded 
  essentially 
  the 
  same 
  results. 
  The 
  determined 
  axial 
  

   ratio 
  c 
  = 
  0*93 
  of 
  borneol 
  is 
  therefore 
  assumed 
  for 
  this 
  substance. 
  

   The 
  observed 
  forms 
  on 
  the 
  normal_type 
  of 
  crystals_are 
  : 
  c, 
  oP 
  

   (0001); 
  s,SU 
  (3031); 
  q, 
  -8K 
  (8081); 
  m, 
  <*> 
  P 
  (1010); 
  and 
  e, 
  

   — 
  4R 
  (40^1). 
  A 
  crystal 
  of 
  this 
  type 
  is 
  represented 
  in 
  figure 
  2. 
  

   The 
  above 
  forms 
  were 
  determined 
  by 
  the 
  following 
  measure- 
  

   ments 
  : 
  

  

  

  Measured. 
  

  

  Average 
  

  

  Ca«, 
  

  

  71° 
  52' 
  

  

  

  

  73 
  24 
  

  

  72° 
  38 
  

  

  Ca?, 
  

  

  81 
  23 
  

  

  

  

  81 
  58 
  

  

  81 
  41 
  

  

  Cy> 
  % 
  m, 
  

  

  90 
  32 
  

  

  90 
  32 
  

  

  Ca6, 
  

  

  75 
  10 
  

  

  75 
  10 
  

  

  72 
  c 
  

  

  46' 
  

  

  82 
  

  

  42 
  

  

  90 
  

  

  08 
  

  

  77 
  

  

  11 
  

  

  The 
  crystals 
  of 
  this 
  substance 
  possessing 
  rhomboidal 
  habit 
  

   represent 
  quite 
  a 
  different 
  crystal 
  combination 
  from 
  the 
  nor- 
  

   mal 
  type 
  of 
  crystals. 
  The 
  prominent 
  forms 
  on 
  these 
  crystals 
  

   (after 
  the 
  base) 
  are 
  the 
  rhombohedron 
  x, 
  fE 
  (5053) 
  and 
  the 
  

  

  