﻿W. 
  P. 
  White 
  — 
  Silicate 
  Specific 
  Heats. 
  43 
  

  

  Several 
  forms 
  of 
  silica, 
  whose 
  expansion 
  is 
  very 
  small, 
  

   and 
  which 
  therefore 
  practically 
  give 
  values 
  of 
  specific 
  

   heat 
  at 
  constant 
  volume, 
  G 
  v 
  , 
  show 
  that 
  C 
  v 
  for 
  high 
  tem- 
  

   peratures 
  appears 
  to 
  exceed 
  the 
  theoretical 
  value 
  5-96. 
  

  

  Glasses 
  show, 
  in 
  the 
  main, 
  a 
  specific 
  heat 
  only 
  slightly 
  

   above 
  the 
  corresponding 
  crystal 
  forms, 
  but 
  with 
  a 
  ten- 
  

   dency 
  to 
  increase 
  at 
  some 
  rather 
  high 
  temperature. 
  

  

  In 
  several 
  sets 
  of 
  polymorphic 
  forms 
  with 
  sluggish 
  

   inversions 
  there 
  were 
  differences 
  of 
  about 
  2 
  per 
  cent 
  

   between 
  the 
  two 
  forms, 
  but 
  none 
  of 
  these 
  forms 
  showed 
  

   any 
  variation 
  in 
  specific 
  heat 
  near 
  the 
  inversion 
  tempera- 
  

   ture. 
  

  

  In 
  quartz, 
  below 
  the 
  a-/3 
  inversion 
  at 
  575°, 
  the 
  heat 
  

   absorption 
  is 
  much 
  less 
  than 
  corresponds 
  to 
  the 
  abnor- 
  

   mal 
  expansion. 
  If 
  such 
  anomalous 
  absorption, 
  unusual 
  

   change 
  of 
  volume, 
  and 
  change 
  of 
  crystal 
  properties 
  are 
  

   each 
  or 
  all 
  together 
  the 
  sign 
  of 
  a 
  change 
  of 
  state, 
  then 
  

   quartz 
  undergoes 
  a 
  gradual 
  change 
  of 
  state 
  over 
  an 
  inter- 
  

   val 
  of 
  400° 
  below 
  what 
  is 
  commonly 
  called 
  its 
  a-/? 
  inver- 
  

   sion. 
  Quartz, 
  and 
  probably 
  other 
  forms 
  of 
  silica, 
  exhibit 
  

   what 
  appear 
  to 
  be 
  two 
  kinds 
  of 
  inversion, 
  due 
  to 
  different 
  

   mechanisms. 
  

  

  Some 
  of 
  these 
  facts 
  militate 
  against 
  certain 
  hypotheses 
  

   which 
  make 
  polymorphism 
  the 
  resultant 
  of 
  continuous 
  

   polymeric 
  or 
  isomeric 
  changes 
  in 
  the 
  solid. 
  

  

  Geophysical 
  Laboratory, 
  

  

  Carnegie 
  Institution 
  of 
  Washington, 
  

   Washington, 
  D. 
  C. 
  

  

  