﻿410 
  N. 
  STORY-MASKELYNE 
  AND 
  AV. 
  FLIGHT 
  ON 
  THE 
  CHARACTER 
  

  

  small 
  an 
  angle 
  as 
  to 
  give 
  a 
  stauroscopic 
  figure 
  almost 
  identical 
  with 
  

   that 
  of 
  a 
  uniaxial 
  crystal. 
  

  

  In 
  parallel 
  light, 
  however, 
  the 
  cleavage-plane 
  exhibits 
  principal 
  

   sections 
  parallel 
  and 
  perpendicular 
  to 
  the 
  edge 
  c, 
  a; 
  and 
  a 
  slight 
  

   opening 
  of 
  the 
  cross 
  perpendicularly 
  to 
  that 
  edge 
  can 
  be 
  detected, 
  so 
  

   that 
  the 
  optic 
  axes 
  would 
  lie 
  in 
  the 
  plane 
  of 
  symmetry. 
  The 
  crystal 
  

   is 
  negative. 
  It 
  hardly 
  exhibits 
  any 
  dichroism 
  for 
  light 
  traversing 
  

   the 
  principal 
  cleavage-plane 
  perpendicularly. 
  

  

  When 
  heated 
  on 
  platinum-foil 
  a 
  little 
  piece 
  expanded 
  to 
  about 
  six 
  

   times 
  its 
  original 
  thickness 
  ; 
  after 
  it 
  has 
  been 
  reduced 
  to 
  powder 
  it 
  

   does 
  not 
  expand 
  at 
  all. 
  By 
  long 
  boiling 
  in 
  strong 
  hydrochloric 
  acid 
  

   it 
  gradually 
  expands, 
  and 
  loses 
  constitutional 
  water 
  at 
  about 
  110° 
  C. 
  

   Heated 
  for 
  many 
  hours 
  at 
  100° 
  C, 
  it 
  apparently 
  underwent 
  no 
  con- 
  

   stitutional 
  change. 
  

  

  The 
  powder 
  dried 
  for 
  an 
  hour 
  and 
  a 
  half 
  at 
  100° 
  C. 
  lost 
  no 
  weight. 
  

   In 
  one 
  portion 
  the 
  loss 
  of 
  weight 
  at 
  higher 
  temperatures 
  was 
  ascer- 
  

   tained 
  ; 
  in 
  another 
  the 
  total 
  amount 
  of 
  water 
  present 
  was 
  directly 
  

   determined. 
  The 
  results 
  are 
  as 
  follow 
  : 
  — 
  

  

  o 
  

  

  o 
  

  

  per 
  cent 
  

  

  iring 
  half 
  an 
  hour 
  at 
  125- 
  

  

  -130 
  C. 
  . 
  

  

  .. 
  1-309 
  

  

  „ 
  half 
  an 
  hour 
  at 
  125- 
  

  

  -130 
  

  

  .. 
  0-205 
  

  

  „ 
  one 
  hour 
  at 
  130 
  

  

  

  .. 
  0-025 
  

  

  „ 
  half 
  an 
  hour 
  at 
  150 
  

  

  

  .. 
  0-231 
  

  

  „ 
  half 
  an 
  hour 
  at 
  150 
  

  

  

  .. 
  0-179 
  

   1-949 
  

  

  Water 
  evolved 
  at 
  a 
  low 
  red 
  heat 
  . 
  

  

  .. 
  9-717 
  

  

  All 
  water 
  which 
  passes 
  off 
  at 
  temperatures 
  about 
  100° 
  C. 
  has 
  been 
  

   regarded 
  as 
  constitutional 
  water. 
  

  

  The 
  mineral 
  has 
  the 
  following 
  composition 
  : 
  — 
  

  

  Oxygen 
  Ratios. 
  

  

  Silicic 
  acid 
  40-833 
  21-777 
  .... 
  10 
  

  

  Alumina 
  9-801 
  4-562 
  1 
  R 
  fi1 
  ft 
  „ 
  

  

  Iron 
  peroxide 
  .... 
  6-844 
  2-054 
  J 
  O'Olb 
  . 
  . 
  . 
  . 
  6 
  

  

  Chromium 
  oxide 
  . 
  . 
  trace. 
  

  

  Magnesia 
  31-338 
  12-535 
  .... 
  6 
  

  

  Soda 
  0-670 
  

  

  Water 
  9-717 
  8-636 
  .... 
  4 
  

  

  Carbonic 
  acid 
  .... 
  trace. 
  

  

  99-203 
  

   The 
  above 
  ratios 
  correspond 
  with 
  the 
  formula 
  

  

  R 
  2 
  3 
  , 
  Si0 
  2 
  +2 
  (3MgO, 
  2Si0 
  2 
  , 
  2H 
  2 
  0). 
  

  

  On 
  comparing 
  the 
  atomic 
  ratios 
  obtained 
  from 
  the 
  analysis 
  of 
  this 
  

   mineral 
  with 
  those 
  given 
  in 
  Prof. 
  Cooke's 
  recently 
  published 
  memoir 
  

   on 
  the 
  Yermiculites*, 
  as 
  those 
  of 
  Jefferisite 
  andHallitef 
  respectively, 
  

  

  * 
  J. 
  P. 
  Cooke, 
  'Proc. 
  Amer. 
  Ac. 
  Arts 
  and 
  Sciences,' 
  December, 
  1873. 
  'Phil. 
  

   Mag.,' 
  April, 
  1874. 
  

  

  t 
  The 
  choice 
  of 
  the 
  name 
  of 
  this 
  mineral 
  is 
  unfortunate, 
  as 
  it 
  is 
  already 
  in 
  

   use 
  as 
  a 
  synonym 
  for 
  the 
  aluminite 
  (Websterite) 
  of 
  Halle. 
  

  

  