﻿N. 
  L. 
  Boijuen 
  — 
  Sodium- 
  Potassium 
  JSfephelites. 
  119 
  

  

  alteration 
  product 
  obtained 
  by 
  Stephenson 
  is 
  very 
  similar 
  to 
  

   if 
  not 
  identical 
  with 
  the 
  twinned 
  form 
  of 
  KAlSi0 
  4 
  .* 
  

  

  Intermediate 
  Mixtures. 
  

  

  By 
  mixing 
  the 
  alkaline 
  carbonates, 
  silica 
  and 
  alumina, 
  in 
  the 
  

   proper 
  proportion, 
  sintering 
  and 
  then 
  fusing, 
  the 
  intermediate 
  

   mixtures 
  containing 
  up 
  to 
  40 
  per 
  cent 
  of 
  the 
  potash 
  compound 
  

   were 
  made 
  satisfactorily. 
  In 
  mixtures 
  richer 
  in 
  potash, 
  however, 
  

   the 
  temperature 
  which 
  must 
  be 
  reached 
  to 
  obtain 
  a 
  homogeneous 
  

   melt 
  is 
  higher 
  so 
  that 
  a 
  little 
  alkali 
  is 
  lost. 
  The 
  loss 
  increases 
  

   as 
  the 
  potash 
  end 
  is 
  approached. 
  An 
  attempt 
  was 
  made 
  to 
  

   avoid 
  this 
  difficulty 
  by 
  using 
  kaliophilite 
  made 
  hydrothermally 
  

   by 
  Morey, 
  and 
  nephelite 
  made 
  in 
  the 
  ordinary 
  way 
  as 
  the 
  ingredi- 
  

   ents 
  of 
  the 
  mixtures. 
  Even 
  with 
  this 
  method 
  the 
  same 
  loss 
  

   of 
  potash 
  was 
  encountered 
  in 
  those 
  mixtures 
  whose 
  melting 
  

   required 
  a 
  high 
  temperature. 
  The 
  results 
  from 
  the 
  potash-rich 
  

   mixtures 
  are, 
  therefore, 
  to 
  some 
  extent 
  unsatisfactory. 
  This 
  

   loss 
  of 
  potash 
  is 
  not, 
  however, 
  so 
  serious 
  as 
  to 
  obscure 
  the 
  rela- 
  

   tionships 
  involved, 
  though 
  it 
  does 
  interfere 
  with 
  the 
  accurate 
  

   fixing 
  of 
  temperatures. 
  

  

  A 
  study 
  of 
  equilibrium 
  in 
  these 
  mixtures 
  w 
  r 
  as 
  made 
  in 
  the 
  

   ordinary 
  way 
  by 
  the 
  method 
  of 
  quenching. 
  Besides 
  the 
  loss 
  

   of 
  potash 
  noted 
  above 
  certain 
  difficulties 
  were 
  encountered 
  in 
  

   the 
  optical 
  determinations 
  which 
  are, 
  perhaps, 
  worthy 
  of 
  note. 
  

   The 
  hexagonal 
  forms 
  of 
  the 
  two 
  components 
  nephelite 
  and 
  

   kaliophilite 
  are 
  so 
  nearly 
  identical 
  in 
  properties 
  that 
  when 
  

   obtained 
  as 
  small 
  crystals 
  embedded 
  in 
  glass, 
  as 
  they 
  are" 
  in 
  

   quenchings, 
  it 
  is 
  impossible 
  to 
  determine 
  whether 
  the 
  crystals 
  

   are 
  kaliophilite 
  or 
  nephelite 
  or 
  of 
  an 
  intermediate 
  composition. 
  

   As 
  a 
  rule 
  in 
  such 
  a 
  case 
  one 
  can 
  obtain 
  a 
  clue 
  to 
  the 
  composi- 
  

   tion 
  of 
  the 
  crystals 
  by 
  determining 
  the 
  composition 
  of 
  the 
  

   glass, 
  but 
  in 
  the 
  present 
  instance 
  the 
  extreme 
  glasses 
  and 
  all 
  

   intermediate 
  glasses 
  have 
  nearly 
  the 
  same 
  refractive 
  indices 
  

   and 
  the 
  composition 
  cannot, 
  therefore, 
  be 
  determined 
  by 
  such 
  

   a 
  method. 
  To 
  determine 
  optically 
  the 
  question 
  of 
  solid 
  solu- 
  

   tion 
  between 
  the 
  components, 
  and 
  its 
  limits, 
  one 
  crystallizes 
  a 
  

   glass 
  of 
  intermediate 
  composition 
  and 
  examines 
  the 
  product 
  

   to 
  see 
  whether 
  it 
  is 
  homogeneous 
  or 
  not. 
  In 
  the 
  present 
  sys- 
  

   tem, 
  however, 
  one 
  cannot 
  determine 
  whether 
  the 
  fine-grained 
  

   product 
  so 
  obtained 
  consists 
  of 
  homogeneous 
  mix-crystals 
  or 
  

   whether 
  kaliophilite 
  and 
  nephelite 
  are 
  present 
  as 
  distinct 
  phases. 
  

  

  Studies 
  of 
  equilibrium 
  are 
  often 
  made 
  in 
  systems 
  of 
  various 
  

   kinds 
  with 
  little 
  observation 
  of 
  the 
  phases 
  themselves. 
  The 
  

   work 
  is 
  almost 
  entirely 
  a 
  measurement 
  of 
  the 
  temperatures 
  at 
  

   which 
  changes 
  of 
  phase 
  take 
  place 
  in 
  various 
  compositions, 
  the 
  

   change 
  being 
  recorded, 
  say, 
  thermally 
  or 
  dilatometrically. 
  

   When 
  these 
  temperatures 
  are 
  plotted 
  against 
  composition 
  it 
  is 
  

  

  * 
  Jour. 
  Geol. 
  xxiv, 
  197, 
  1916. 
  

  

  