﻿290 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  12 
  

  

  the 
  axial 
  ratio 
  given 
  at 
  the 
  head 
  of 
  the 
  angle 
  table 
  is 
  the 
  result. 
  Fe- 
  

   dorov 
  termed 
  the 
  orientations 
  worked 
  out 
  on 
  the 
  basis 
  of 
  his 
  rules 
  the 
  

   "correct 
  setting," 
  but 
  any 
  one 
  of 
  the 
  six 
  orientations 
  of 
  an 
  orthorhom- 
  

   bic 
  crystal 
  is 
  just 
  as 
  correct 
  as 
  any 
  other, 
  so 
  the 
  term 
  "significant" 
  is 
  

   preferred, 
  since 
  what 
  is 
  meant 
  is 
  that 
  orientation 
  which 
  best 
  brings 
  

   out 
  the 
  relations 
  of 
  the 
  crystal 
  to 
  other 
  systems. 
  

  

  TABLE 
  2. 
  — 
  Angles 
  of 
  calcium 
  fumarate 
  in 
  significant 
  orientation 
  

   Orthorhombic; 
  a:b 
  -.c 
  = 
  1.0523 
  : 
  1 
  : 
  2.6510 
  (po 
  = 
  2.5193; 
  qo 
  = 
  2.6510). 
  Peritetrag- 
  

   onal, 
  with 
  deviation 
  of 
  prism 
  angle 
  <p 
  from 
  the 
  tetragonal 
  value 
  = 
  1 
  °28'. 
  

  

  Description 
  

   Dominant 
  form 
  

   Narrow 
  but 
  brilliant 
  

   Like 
  e, 
  but 
  longer 
  

   (Calculated) 
  

  

  The 
  crystals 
  are 
  usually 
  distorted 
  in 
  such 
  a 
  manner 
  that 
  one 
  dome 
  

   face 
  of 
  each 
  pair 
  is 
  decidedly 
  larger 
  than 
  the 
  other, 
  the 
  symmetry 
  be- 
  

   ing 
  thus 
  ecto-hemimorphic. 
  Their 
  average 
  habit 
  is 
  shown 
  in 
  Figure 
  1. 
  

  

  Space 
  relations. 
  — 
  The 
  topic 
  axes 
  of 
  the 
  substance 
  were 
  next 
  cal- 
  

   culated. 
  As 
  the 
  usual 
  plan 
  for 
  doing 
  this 
  obscures 
  the 
  relations 
  some- 
  

   what, 
  it 
  becomes 
  preferable 
  to 
  first 
  calculate 
  unit-volume 
  axes, 
  which 
  

   differ 
  from 
  the 
  usual 
  crystal 
  axes 
  in 
  that 
  axis 
  b 
  is 
  no 
  longer 
  taken 
  as 
  

   unity, 
  but 
  is 
  reduced 
  to 
  such 
  a 
  value 
  that 
  the 
  product 
  of 
  all 
  their 
  axes 
  

   equals 
  one. 
  The 
  unit 
  volume 
  axes 
  may 
  be 
  distinguished 
  from 
  the 
  

   ordinary 
  axes 
  by 
  the 
  use 
  of 
  capital 
  letters. 
  The 
  formulas 
  used 
  are: 
  

   A 
  = 
  '^a'^/c; 
  B 
  = 
  A/a; 
  C 
  = 
  c 
  X 
  B. 
  Using 
  the 
  values 
  obtained 
  from 
  

   the 
  significant 
  orientation 
  of 
  Table 
  2, 
  the 
  results 
  are: 
  A 
  : 
  B 
  : 
  C 
  = 
  

   0.7475 
  : 
  0.7104 
  : 
  1.8832. 
  

  

  The 
  molecular 
  weight 
  of 
  calcium 
  fumarate, 
  Ca(C4H204) 
  .2H2O, 
  is 
  

   190.1. 
  Its 
  specific 
  gravity 
  was 
  determined 
  by 
  suspending 
  a 
  few 
  

   crystals 
  in 
  a 
  mixture 
  of 
  carbon 
  tetrachloride 
  and 
  bromoform, 
  the 
  

   amounts 
  of 
  the 
  constituents 
  being 
  varied 
  until 
  the 
  crystals 
  remained 
  

   suspended, 
  when 
  the 
  specific 
  gravity 
  of 
  the 
  liquid 
  was 
  obtained 
  with 
  

   a 
  Westphal 
  balance. 
  As 
  variation 
  from 
  one 
  crystal 
  to 
  another 
  was 
  

   shown, 
  some 
  floating 
  in 
  the 
  same 
  liquid 
  in 
  which 
  others 
  sank, 
  it 
  would 
  

   be 
  meaningless 
  to 
  state 
  the 
  result 
  beyond 
  the 
  second 
  place; 
  it 
  was 
  

   1.71 
  =<= 
  0.01. 
  The 
  molecular 
  volume 
  is 
  accordingly 
  111.2 
  and 
  the 
  

   cube 
  root 
  of 
  it 
  4.81. 
  Multiplying 
  the 
  unit-volume 
  axes 
  by 
  this 
  fac- 
  

   tor, 
  the 
  topic 
  axes 
  are 
  : 
  x 
  '• 
  '4^ 
  '■ 
  ^ 
  = 
  3.60 
  : 
  3.42 
  : 
  9.06. 
  

  

  Optical 
  properties. 
  — 
  Study 
  by 
  the 
  immersion 
  method 
  under 
  the 
  

   polarizing 
  microscope 
  shows 
  calcium 
  fumarate 
  to 
  be 
  biaxial 
  negative 
  

  

  