﻿336 
  Fenner 
  — 
  Stability 
  delations 
  of 
  Silica 
  Minerals. 
  

  

  inversion-point 
  the 
  velocity 
  of 
  transformation 
  was 
  extremely 
  

   small 
  and 
  a 
  long 
  period 
  of 
  heating 
  was 
  required 
  to 
  insure 
  the 
  

   appearance 
  of 
  the 
  stable 
  phase, 
  but 
  outside 
  of 
  this 
  range 
  a 
  

   noticeably 
  less 
  time 
  was 
  required. 
  Fine 
  grinding 
  apparently 
  

   did 
  not 
  increase 
  the 
  velocity 
  of 
  the 
  reaction. 
  

  

  As 
  the 
  range 
  within 
  which 
  the 
  inversion 
  lay 
  was 
  gradually 
  

   narrowed 
  down 
  great 
  care 
  was 
  exercised 
  in 
  the 
  regulation 
  of 
  

   furnace 
  temperature. 
  The 
  method 
  of 
  procedure 
  was 
  to 
  hold 
  

   the 
  charge 
  for 
  a 
  long 
  period 
  at 
  some 
  temperature 
  previously 
  

   decided 
  upon, 
  keeping 
  close 
  watch 
  to 
  see 
  that 
  some 
  unexpected 
  

   variation 
  in 
  the 
  strength 
  of 
  the 
  heating 
  current 
  did 
  not 
  cause 
  a 
  

   departure 
  from 
  this 
  temperature. 
  When 
  necessary 
  to 
  continue 
  

   heating 
  from 
  one 
  day 
  to 
  the 
  next 
  (as 
  was 
  frequently 
  the 
  case) 
  

   the 
  current 
  from 
  the 
  generator 
  was 
  replaced 
  by 
  that 
  from 
  stor- 
  

   age 
  batteries. 
  These 
  batteries 
  possessed 
  very 
  constant 
  voltage 
  

   and 
  were 
  of 
  such 
  capacity 
  that 
  in 
  a 
  run 
  of 
  fifteen 
  or 
  sixteen 
  

   hours 
  the 
  temperature 
  of 
  the 
  furnace 
  dropped 
  only 
  8-10 
  

   degrees. 
  

  

  A 
  description 
  of 
  several 
  of 
  the 
  more 
  significant 
  experiments 
  

   follows 
  : 
  

  

  No. 
  82. 
  A 
  mixture 
  of 
  finely 
  ground 
  silica 
  glass 
  with 
  sodic 
  

   tungstate 
  ; 
  length 
  of 
  heating, 
  11 
  hours 
  20 
  minutes, 
  during 
  

   which 
  the 
  temperature 
  was 
  kept 
  very 
  close 
  to 
  865°, 
  extreme 
  

   variations 
  863°-875°. 
  The 
  product 
  was 
  essentially 
  tridymite, 
  

   but 
  distinct 
  quartz 
  grains 
  were 
  found, 
  often 
  with 
  bipyramidal 
  

   terminations. 
  (As 
  will 
  appear 
  a 
  little 
  later, 
  the 
  tridymite 
  was 
  

   an 
  intermediate 
  stage, 
  and 
  the 
  point 
  of 
  significance 
  is 
  the 
  fact 
  

   that 
  it 
  was 
  changing 
  to 
  quartz 
  at 
  this 
  temperature.) 
  

  

  No. 
  102. 
  A 
  mixture 
  of 
  artificial 
  tridymite 
  and 
  sodic 
  tung- 
  

   state 
  ; 
  length 
  of 
  heating, 
  73-J 
  hours 
  ; 
  utmost 
  variation, 
  854°- 
  

   864° 
  ; 
  general 
  temperature, 
  858°. 
  The 
  product 
  was 
  still 
  mostly 
  

   tridymite, 
  but 
  there 
  were 
  very 
  numerous 
  quartz 
  crystals, 
  

   mostly 
  as 
  nuclei 
  of 
  tridymite 
  aggregates. 
  

  

  No. 
  103. 
  Ground 
  quartz 
  with 
  sodic 
  tungstate 
  ; 
  length 
  of 
  

   heating, 
  24 
  hours 
  ; 
  general 
  temperature, 
  875° 
  ; 
  range, 
  865°- 
  

   877° 
  ; 
  product, 
  quartz 
  with 
  considerable 
  tridymite 
  in 
  hexagonal 
  

   plates. 
  

  

  Other 
  experiments 
  of 
  the 
  same 
  nature 
  might 
  be 
  described, 
  

   confirming 
  the 
  above 
  results 
  and 
  fixing 
  the 
  temperature 
  of 
  

   inversion 
  at 
  a 
  point 
  very 
  close 
  to 
  870°. 
  

  

  Because 
  of 
  the 
  great 
  difficulty 
  of 
  keeping 
  the 
  temperature 
  

   of 
  the 
  furnace 
  constant 
  for 
  such 
  a 
  length 
  of 
  time, 
  some 
  latitude 
  

   must 
  be 
  permitted 
  in 
  expressing 
  the 
  temperature 
  of 
  inversion, 
  

   but 
  it 
  is 
  believed 
  to 
  lie 
  within 
  10° 
  of 
  870°. 
  

  

  It 
  has 
  not 
  been 
  considered 
  necessary 
  to 
  tabulate 
  the 
  results 
  

   of 
  experiments 
  conducted 
  much 
  above 
  or 
  below 
  870°, 
  for 
  at 
  

   such 
  temperatures 
  quartz 
  changed 
  to 
  tridymite 
  in 
  the 
  one 
  case 
  

   and 
  tridymite 
  to 
  quartz 
  in 
  the 
  other 
  in 
  an 
  unequivocal 
  manner. 
  

  

  