﻿JUNE 
  19, 
  1922 
  WHERRY 
  AND 
  hann: 
  calcium 
  fumarate 
  and 
  maleate 
  289 
  

  

  describer; 
  and 
  in 
  the 
  present 
  substance 
  the 
  single 
  pinacoid 
  present 
  

   might 
  be 
  made 
  either 
  a, 
  h, 
  or 
  c, 
  while 
  in 
  each 
  of 
  these 
  cases 
  the 
  dome- 
  

   prism 
  forms 
  might 
  be 
  placed 
  in 
  either 
  of 
  two 
  positions. 
  The 
  conven- 
  

   tional 
  rule 
  about 
  such 
  matters 
  is 
  to 
  place 
  the 
  direction 
  of 
  greatest 
  elonga- 
  

   tion 
  vertical, 
  and 
  make 
  a 
  dominant 
  pinacoid 
  face 
  h. 
  When 
  this 
  is 
  

   done 
  for 
  calcium 
  fumarate, 
  its 
  angle 
  data 
  come 
  out 
  as 
  shown 
  in 
  Table 
  1. 
  

  

  TABLE 
  1. 
  — 
  Angles 
  of 
  calcium 
  fumarate 
  in 
  conventional 
  orientation. 
  

   Orthorhombic; 
  a 
  : 
  b 
  : 
  c 
  = 
  0.3970 
  : 
  1 
  : 
  0.3772 
  (po 
  = 
  0.9503; 
  qo 
  = 
  0.3772). 
  

  

  Number 
  Symbols 
  Angles 
  Observed 
  

  

  Letter 
  Gdt. 
  Mill. 
  Description 
  >p 
  p 
  

  

  lb 
  Ox 
  010 
  Dominant 
  form 
  0°00' 
  90°00' 
  

  

  2 
  m 
  00 
  110 
  Longer 
  marginal 
  form 
  68°21' 
  90°00' 
  

  

  3 
  q 
  01 
  Oil 
  Shorter 
  marginal 
  form 
  0°00' 
  20°40' 
  

  

  It 
  may 
  be 
  noted 
  that 
  this 
  substance 
  lies 
  very 
  near 
  to 
  the 
  mineral 
  

   columbite, 
  FeCb206, 
  which, 
  in 
  corresponding 
  orientation, 
  has 
  a 
  : 
  5 
  -.c 
  = 
  

   0.4023 
  : 
  1 
  : 
  0.3580. 
  

  

  There 
  is, 
  however, 
  another 
  method 
  of 
  orientation 
  which 
  in 
  many 
  

   respects 
  seem 
  preferable, 
  namely, 
  that 
  worked 
  out 
  by 
  the 
  late 
  Professor 
  

   E. 
  S. 
  Fedorov.- 
  Unfortunately 
  his 
  rules 
  have 
  not 
  yet 
  been 
  made 
  

   available 
  to 
  non-Russian 
  readers 
  in 
  complete 
  form. 
  The 
  first 
  step 
  

   seems 
  to 
  be 
  to 
  bring 
  the 
  crystal 
  into 
  that 
  orientation 
  which 
  shall 
  

   show 
  most 
  clearly 
  its 
  relationship 
  to 
  a 
  system 
  of 
  higher 
  symmetry. 
  

   In 
  the 
  present 
  case, 
  it 
  takes 
  but 
  brief 
  inspection 
  of 
  the 
  habit 
  to 
  realize 
  

   that 
  this 
  substance 
  approaches 
  the 
  tetragonal 
  system 
  if 
  the 
  large 
  pin- 
  

   acoid 
  is 
  made 
  the 
  base, 
  and 
  this 
  is 
  the 
  orientation 
  adopted 
  for 
  the 
  

   second 
  angle 
  table. 
  The 
  substance 
  is, 
  in 
  fact, 
  as 
  far 
  as 
  the 
  angles 
  go, 
  

   markedly 
  peri 
  tetragonal. 
  According 
  to 
  Fedorov,^ 
  the 
  tabular 
  habit 
  

   perpendicular 
  to 
  axis 
  c 
  indicates 
  that 
  the 
  axial 
  ratio 
  should 
  be 
  strongly 
  

   positive 
  — 
  ^that 
  is, 
  axis 
  c 
  should 
  be 
  much 
  greater 
  than 
  the 
  others. 
  As 
  

   a 
  matter 
  of 
  fact, 
  whichever 
  axis 
  is 
  taken 
  as 
  b, 
  the 
  value 
  of 
  c 
  is 
  greater 
  

   than 
  2V2, 
  so 
  that 
  thus 
  far 
  the 
  relations 
  are 
  normal. 
  

  

  Next 
  there 
  is 
  a 
  choice 
  between 
  making 
  the 
  dome 
  with 
  the 
  smaller 
  

   rho 
  angle 
  the 
  side 
  dome 
  or 
  the 
  front 
  dome; 
  in 
  the 
  former 
  position, 
  

   axis 
  a 
  would 
  be 
  less 
  than 
  axis 
  b, 
  in 
  the 
  latter, 
  greater 
  than 
  b. 
  Since 
  b 
  

   is 
  by 
  convention 
  taken 
  as 
  the 
  unit 
  axis, 
  it 
  seems 
  preferable 
  to 
  make 
  a 
  

   greater 
  than 
  b, 
  and 
  as 
  this 
  also 
  agrees 
  with 
  Fedorov' 
  s 
  rule, 
  the 
  greater 
  

   elongation 
  of 
  the 
  crystal 
  being 
  toward 
  the 
  greater 
  rho, 
  the 
  dome 
  with 
  

   the 
  smaller 
  rho 
  angle 
  has 
  been 
  turned 
  to 
  the 
  front, 
  that 
  is, 
  made 
  form 
  

   (101). 
  The 
  dome 
  with 
  the 
  larger 
  rho 
  angle 
  then 
  becomes 
  (Oil), 
  and 
  

  

  2 
  Z. 
  Kryst. 
  Min. 
  50: 
  513. 
  1912. 
  

   ^ 
  Loc. 
  cit. 
  

  

  