﻿450 
  Hobbs 
  — 
  Crystal 
  Form 
  of 
  Borneol 
  and 
  Isoborneol. 
  

  

  no 
  one 
  occurs 
  in 
  both 
  positive 
  and 
  negative 
  dodeeants 
  on 
  the 
  

   same 
  crystal. 
  The 
  habit 
  of 
  both 
  substances 
  is 
  broadly 
  tabular 
  

   parallel 
  to 
  the 
  basal 
  pinacoid 
  and 
  the 
  plates 
  have 
  generally 
  a 
  

   regular 
  hexagonal 
  outline. 
  One 
  variety 
  of 
  isoborneol 
  is, 
  how- 
  

   ever, 
  observed 
  whose 
  crystals 
  take 
  the 
  form 
  of 
  rhomboidal 
  

   plates 
  owing 
  to 
  the 
  disappearance 
  of 
  all 
  planes 
  from 
  two 
  of 
  the 
  

   opposite 
  vertical 
  pairs 
  of 
  dodecants. 
  Although 
  these 
  crystals 
  

   are 
  identical 
  with 
  the 
  normal 
  variety 
  in 
  regard 
  to 
  their 
  optical 
  

   properties, 
  they 
  nevertheless 
  represent 
  an 
  entirely 
  different 
  

   crystal 
  combination. 
  Crystals 
  from 
  all 
  the 
  samples 
  have 
  their 
  

   faces 
  more 
  or 
  less 
  rounded 
  and 
  the 
  measurements 
  are 
  as 
  a 
  

   result 
  subject 
  to 
  considerable 
  variations, 
  but 
  they 
  are, 
  neverthe- 
  

   less 
  sufficiently 
  accurate 
  for 
  a 
  determination 
  of 
  all 
  the 
  forms. 
  

   It 
  is 
  very 
  probable 
  that 
  the 
  axial 
  ratios 
  of 
  borneol 
  and 
  isobor- 
  

   neol 
  are 
  different, 
  since 
  the 
  substances 
  differ 
  so 
  much 
  in 
  their 
  

   double 
  refraction, 
  but 
  they 
  are 
  certainly 
  nearly 
  identical 
  and 
  

   the 
  difference 
  is 
  within 
  the 
  limits 
  of 
  error 
  in 
  the 
  reading 
  of 
  

   angles 
  on 
  the 
  crystals 
  examined. 
  I 
  have 
  therefore 
  used 
  for 
  

   both 
  substances 
  the 
  axial 
  ratio 
  determined 
  on 
  crystals 
  of 
  bor- 
  

   neol 
  from 
  Picea 
  nigra. 
  

  

  Borneol 
  from 
  Picea 
  nigra. 
  The 
  crystals 
  of 
  this 
  substance 
  

   examined 
  are 
  thin, 
  colorless, 
  hexagonal 
  plates 
  having 
  a 
  diameter 
  

   of 
  J-l 
  cm 
  . 
  and 
  a 
  thickness 
  of 
  0*5- 
  I 
  mm 
  . 
  The 
  larger 
  plates 
  have 
  a 
  

   wide 
  peripheral 
  zone 
  which 
  is 
  occupied 
  by 
  cavities 
  generally 
  filled 
  

   with 
  mother 
  liquor. 
  The 
  shape 
  of 
  these 
  cavities 
  is 
  somewhat 
  

   irregular, 
  but 
  they 
  are 
  oriented 
  roughly 
  parallel 
  to 
  the 
  bounda- 
  

   ries 
  of 
  the 
  plate. 
  Besides 
  the 
  basal 
  pinacoid 
  the 
  prominent 
  forms 
  

   are 
  a 
  steep 
  rhombohedron 
  making 
  nearly 
  83° 
  with 
  the 
  base 
  and 
  a 
  

   smaller 
  rhombohedral 
  face 
  of 
  opposite 
  sign 
  which 
  makes 
  nearly 
  

   73° 
  with 
  the 
  same 
  form. 
  This 
  latter 
  form 
  is 
  undoubtedly 
  the 
  

   pyramid 
  observed 
  on 
  the 
  substance 
  by 
  Traube 
  and 
  it 
  is 
  there- 
  

   fore 
  chosen 
  for 
  determining 
  the 
  axial 
  ratio. 
  The 
  average 
  of 
  four 
  

   measurements 
  of 
  the 
  angle 
  included 
  between 
  this 
  face 
  and 
  the 
  

   base 
  (limits 
  71° 
  25 
  7 
  and 
  74° 
  6') 
  is 
  72° 
  W 
  and 
  if 
  considered 
  the 
  

   fundamental 
  rhombohedron 
  the 
  axial 
  ratio 
  would 
  be 
  c 
  = 
  2*79 
  

   (2*83, 
  Traube). 
  It 
  is, 
  however, 
  more 
  convenient 
  to 
  consider 
  

   this 
  form 
  3R 
  (3031), 
  which 
  makes 
  the 
  axial 
  ratio 
  c_= 
  0*93. 
  

  

  The 
  observed 
  forms 
  are 
  c, 
  oP 
  (0001) 
  ; 
  *, 
  3R 
  (3031) 
  ; 
  q, 
  -8R 
  

   (8081) 
  ; 
  m, 
  oo 
  P 
  (1010) 
  ; 
  t, 
  f 
  R 
  (2023) 
  ; 
  u, 
  4R 
  (4041). 
  Figure 
  1 
  

   represents 
  a 
  crystal 
  of 
  borneol. 
  These 
  forms 
  have 
  been 
  deter- 
  

   mined 
  by 
  the 
  following 
  measurements 
  : 
  

  

  

  Measured. 
  

  

  

  

  Calculated. 
  

  

  C/\S, 
  

  

  72° 
  46' 
  

  

  (limits 
  71° 
  25' 
  

  

  and 
  74° 
  6') 
  

  

  72° 
  46' 
  

  

  ca?, 
  

  

  82 
  42 
  

  

  (limits 
  81 
  13 
  

  

  and 
  83 
  47 
  ) 
  

  

  83 
  22 
  

  

  c^m, 
  

  

  90 
  6 
  

  

  

  

  90 
  

  

  Cy\U, 
  

  

  77 
  11 
  

  

  (limits 
  76 
  47 
  

  

  and 
  77 
  35 
  ) 
  

  

  76 
  54 
  

  

  C,\t, 
  

  

  34 
  38 
  

  

  

  

  35 
  37 
  

  

  