﻿28 
  W. 
  P. 
  White 
  — 
  Silicate 
  Specific 
  Heats. 
  

  

  a. 
  Magnesium 
  metasilicate 
  in 
  the 
  amphibole 
  form 
  is 
  

   metastable, 
  undergoing 
  at 
  a 
  temperature 
  high 
  enough 
  to 
  

   release 
  the 
  molecular 
  rigidity 
  (say, 
  1300°) 
  a 
  monotropic 
  

   inversion 
  into 
  pyroxene 
  with 
  evolution 
  of 
  heat. 
  This 
  

   unstable 
  form 
  has 
  a 
  specific 
  heat 
  over 
  1% 
  below 
  the 
  other. 
  

   Here 
  the 
  form 
  of 
  greater 
  specific 
  volume 
  (of 
  less 
  

   density), 
  namely, 
  the 
  amphibole, 
  has 
  the 
  smaller 
  specific 
  

   heat, 
  contrary 
  to 
  Richarz' 
  rule. 
  31 
  It 
  is 
  of 
  course 
  possible 
  

   that 
  the 
  difference 
  in 
  the 
  atomic 
  heat 
  of 
  these 
  forms 
  of 
  

   magnesium 
  metasilicate 
  is 
  due 
  to 
  a 
  difference 
  in 
  the 
  rate 
  

   of 
  expansion, 
  i. 
  e., 
  that 
  there 
  is 
  no 
  difference 
  in 
  the 
  atomic 
  

   heat 
  at 
  constant 
  volume. 
  

  

  b. 
  Wollastonite 
  (Calcium 
  metasilicate) 
  undergoes 
  at 
  

   the 
  definite 
  temperature 
  1170° 
  an 
  enantiotropic 
  inver- 
  

   sion 
  into 
  pseudo-wollastonite 
  with 
  absorption 
  of 
  heat, 
  

   about 
  10 
  calories 
  per 
  gram. 
  32 
  The 
  high 
  temperature 
  

   form, 
  pseudo-wollastonite, 
  has 
  a 
  lower 
  specific 
  heat. 
  

   The 
  transformation 
  is 
  sluggish 
  and 
  the 
  reverse 
  trans- 
  

   formation 
  on 
  cooling 
  does 
  not 
  take 
  place 
  at 
  all 
  without 
  the 
  

   assistance 
  of 
  a 
  solvent. 
  The 
  pseudo-wollastonite 
  was 
  in 
  

   fact 
  investigated 
  down 
  to 
  100°. 
  It 
  retains 
  the 
  lower 
  

   specific 
  heat 
  down 
  at 
  least 
  to 
  700°. 
  Here 
  it 
  is 
  metastable, 
  

   and 
  would 
  change 
  into 
  wollastonite 
  with 
  evolution 
  of 
  

   heat 
  but 
  for 
  the 
  sluggishness. 
  Neither 
  form 
  shows 
  any 
  

   perceptible 
  irregularity 
  in 
  its 
  specific 
  heat 
  curve 
  near 
  

   the 
  temperature 
  of 
  inversion, 
  though 
  wollastonite 
  was 
  

   carried 
  within 
  10° 
  of 
  that 
  temperature, 
  and 
  pseudo-wol- 
  

   lastonite 
  was 
  carried 
  through 
  it. 
  

  

  c. 
  Quartz 
  undergoes 
  a 
  reversible, 
  or 
  enantiotropic, 
  

   inversion 
  at 
  575°, 
  from 
  a-quartz 
  to 
  ^-quartz, 
  which 
  is 
  very 
  

   sharp 
  and 
  prompt 
  on 
  both 
  falling 
  and 
  rising 
  tempera- 
  

   ture. 
  Randall, 
  33 
  Day, 
  Sosman, 
  and 
  Hostetter, 
  34 
  Rinne 
  

  

  31 
  Richarz' 
  rule 
  (Wied. 
  Ann., 
  48, 
  708, 
  1893) 
  in 
  strictness 
  only 
  applies 
  

   to 
  elements, 
  but 
  it 
  has 
  also 
  been 
  supposed 
  to 
  hold 
  for 
  most 
  compounds. 
  

   But 
  Bridgman's 
  results, 
  referred 
  to 
  later, 
  seem 
  to 
  contradict 
  this 
  supposition 
  

   very 
  completely. 
  

  

  32 
  E. 
  T. 
  Allen, 
  W. 
  P. 
  White 
  and 
  F. 
  E. 
  Wright, 
  On 
  Wollastonite 
  and 
  Pseudo- 
  

   Wollastonite, 
  this 
  Journal, 
  21, 
  93, 
  1906; 
  Walter 
  P. 
  White, 
  Melting 
  Point 
  

   Methods 
  at 
  High 
  Temperatures, 
  ibid., 
  28, 
  486, 
  1909; 
  republished 
  in 
  Zs. 
  

   anorg. 
  Chem., 
  69, 
  348, 
  1911. 
  

  

  II. 
  M. 
  Randall, 
  On 
  the 
  Coefficient 
  of 
  Expansion 
  of 
  Quartz, 
  Phys. 
  Rev., 
  

   20, 
  10, 
  1905. 
  

  

  34 
  Arthur 
  L. 
  Day, 
  R. 
  B. 
  Sosman, 
  and 
  J. 
  C. 
  Hostetter, 
  The 
  Determination 
  

   of 
  Mineral 
  and 
  Rock 
  Densities 
  at 
  High 
  Temperatures, 
  this 
  Journal, 
  37, 
  

   1, 
  1914. 
  

  

  