﻿JV. 
  L. 
  Bowen 
  — 
  Sodium-Potassium 
  JSejphelites. 
  123 
  

  

  sions 
  no 
  sintering 
  of 
  the 
  powdered 
  charge. 
  On 
  raising 
  the 
  

   temperature 
  further, 
  however, 
  a 
  point 
  is 
  finally 
  reached 
  at 
  

   which 
  rapid 
  increase 
  of 
  glass 
  takes 
  place 
  for 
  only 
  a 
  few 
  degrees 
  

   rise 
  of 
  temperature. 
  This 
  glass 
  has, 
  moreover, 
  quite 
  different 
  

   properties. 
  It 
  evidently 
  flows 
  comparatively 
  freely 
  and 
  fills 
  

   all 
  the 
  interstices 
  of 
  the 
  powdered 
  charge 
  which 
  becomes, 
  even 
  

   to 
  the 
  naked 
  eye, 
  obviously 
  semi-vitreous. 
  This 
  temperature 
  

  

  Fig. 
  1. 
  

  

  

  

  

  

  

  

  

  

  

  

  

  1700 
  

  

  

  

  

  

  

  

  

  

  s 
  

  

  

  

  

  

  

  

  

  

  / 
  

  

  / 
  

  

  

  1600 
  

  

  

  

  

  

  

  

  / 
  

  

  * 
  

  

  

  

  

  

  

  

  

  / 
  

  

  f 
  

  

  / 
  

   / 
  

  

  

  

  1500 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  1400 
  

  

  

  ^-^_— 
  (■ 
  

  

  1 
  fYTf( 
  

  

  * 
  Pi 
  

  

  

  

  

  

  

  

  

  

  x 
  

  

  s 
  

  

  

  

  

  

  

  

  1300 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  1200 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  NaAlSi0 
  4 
  10 
  

  

  20 
  

  

  30 
  

  

  40 
  50 
  

  

  WT. 
  PER 
  CE 
  NT 
  

  

  60 
  

  

  70 
  

  

  80 
  90 
  

  

  KAlSiO„ 
  

  

  at 
  which 
  rapid 
  increase 
  of 
  glass 
  is 
  first 
  observed 
  is 
  regarded 
  as 
  

   the 
  true 
  temperature 
  of 
  beginning 
  of 
  melting. 
  

  

  The 
  method 
  involves 
  the 
  personal 
  equation 
  to 
  some 
  extent. 
  

   The 
  temperature 
  is 
  probably 
  somewhat 
  lower 
  than 
  that 
  which 
  

   the 
  true 
  composition 
  would 
  show. 
  Nevertheless 
  there 
  can 
  be 
  

   no 
  question 
  that 
  the 
  true 
  curve 
  w 
  T 
  ould 
  have 
  a 
  steep 
  slope 
  and 
  

   approximate 
  in 
  position 
  the 
  determined 
  curve 
  shown 
  in 
  fig. 
  1. 
  

  

  The 
  temperature 
  of 
  completion 
  of 
  melting 
  of 
  these 
  somewhat 
  

   impure 
  mixtures 
  is 
  easily 
  determined 
  in 
  the 
  ordinary 
  manner. 
  

   On 
  account 
  of 
  deviation 
  of 
  the 
  mixtures 
  from 
  the 
  true 
  com- 
  

   position 
  the 
  various 
  points 
  are 
  somewhat 
  too 
  low, 
  no 
  doubt. 
  

   The 
  effect 
  of 
  a 
  small 
  amount 
  of 
  impurity 
  in 
  lowering 
  the 
  tern- 
  

  

  