﻿W. 
  P. 
  White 
  — 
  Silicate 
  Specific 
  Heats. 
  

  

  33 
  

  

  crystal, 
  we 
  may 
  have 
  instead 
  of 
  the 
  pure 
  component 
  at 
  Y 
  

   the 
  mix 
  crystal 
  X, 
  containing 
  both 
  A 
  and 
  B. 
  For 
  a 
  dif- 
  

   ferent 
  composition, 
  as 
  V 
  1? 
  the 
  temperature 
  at 
  which 
  

   crystallization 
  begins 
  will 
  generally 
  be 
  different, 
  as 
  W 
  x 
  ; 
  

   the 
  line, 
  NP, 
  is 
  the 
  locus 
  of 
  the 
  points 
  representing 
  such 
  

   temperatures 
  and 
  compositions, 
  and, 
  similarly, 
  NQ 
  repre- 
  

   sents 
  the 
  resulting 
  solids. 
  NP 
  and 
  NQ 
  are 
  thus 
  lines 
  

   marking 
  the 
  compositions 
  of 
  liquid 
  and 
  solid 
  which 
  at 
  

   each 
  temperature 
  are 
  in 
  equilibrium 
  with 
  each 
  other; 
  

   that 
  is, 
  which 
  can 
  exist 
  in 
  contact 
  indefinitely. 
  The 
  

  

  Fig. 
  3. 
  

  

  Concentration 
  

  

  equilibrium 
  is 
  a 
  question 
  of 
  solution. 
  This 
  is 
  not 
  a 
  

   theory 
  of 
  the 
  changes, 
  merely 
  a 
  statement 
  of 
  them. 
  

  

  From 
  the 
  above 
  there 
  follows 
  an 
  important 
  corollary 
  as 
  

   to 
  the 
  progress 
  of 
  a 
  solidification. 
  The 
  abstraction 
  from 
  

   the 
  solution 
  of 
  material 
  of 
  composition 
  X 
  makes 
  the 
  

   remaining 
  liquid 
  richer 
  in 
  the 
  other 
  component, 
  so 
  that 
  

   further 
  crystallization 
  takes 
  place 
  from 
  this 
  altered 
  

   liquid 
  and 
  at 
  a 
  correspondingly 
  altered 
  temperature 
  ; 
  the 
  

   composition 
  and 
  temperature 
  thus 
  move 
  down 
  the 
  line 
  

   NP, 
  with 
  corresponding 
  changes 
  in 
  the 
  solid. 
  

  

  Am. 
  Jour. 
  Sci. 
  — 
  Fourth 
  Series, 
  Vol. 
  XLVII, 
  No. 
  277.— 
  January, 
  1919.. 
  

   3 
  

  

  