﻿172 
  

  

  C. 
  Bancs 
  — 
  Hot 
  Water 
  and 
  Soft 
  Glass 
  

  

  other, 
  and 
  the 
  attraction 
  of 
  solid 
  and 
  liquid 
  molecules 
  may 
  be 
  

   symbolized 
  by 
  FF, 
  SS, 
  and 
  FS, 
  respectively. 
  Of 
  these 
  groups 
  

   FF+SS 
  together 
  promote 
  precipitation 
  or 
  crystallization, 
  while 
  

   FS 
  alone 
  is 
  favorable 
  to 
  solution. 
  The 
  former 
  case 
  occurs 
  for 
  

   FF+SS>F8; 
  the 
  latter 
  for 
  FF+8S<FS. 
  FF+SS=FS 
  

   for 
  a 
  given 
  diameter 
  of 
  particle 
  is 
  the 
  stable 
  case. 
  Suppose 
  

  

  now 
  the 
  diameter 
  of 
  the 
  particle 
  is 
  laid 
  off 
  horizontally, 
  and 
  

   the 
  forces 
  in 
  question 
  are 
  laid 
  off 
  vertically. 
  We 
  obtain 
  two 
  

   curves 
  which 
  must 
  intersect 
  and 
  have 
  the 
  relations 
  to 
  each 
  

   other 
  given 
  by 
  the 
  figure, 
  if 
  a 
  definite 
  diameter 
  2r 
  larger 
  than 
  

   the 
  molecular 
  diameter 
  2r 
  m 
  is 
  to 
  be 
  stable. 
  ' 
  For 
  larger 
  particles 
  

   the 
  forces 
  FS 
  are 
  in 
  excess 
  and 
  the 
  particle 
  will 
  dwindle 
  by 
  

   solution. 
  For 
  smaller 
  particles 
  the 
  forces 
  FF+SS 
  are 
  in 
  

   excess, 
  and 
  the 
  particle 
  will 
  grow 
  by 
  accretion. 
  The 
  effect 
  of 
  

   temperature 
  is 
  to 
  shift 
  the 
  curves 
  relatively 
  to 
  each 
  other, 
  tem- 
  

   perature 
  increase 
  tending 
  to 
  raise 
  SF 
  and 
  to 
  lower 
  FF+SS, 
  

   simultaneously. 
  Recalling 
  the 
  colloidal 
  condition 
  r 
  >r 
  m 
  , 
  the 
  

   result 
  is 
  a 
  motion 
  of 
  the 
  point 
  of 
  intersection 
  to 
  the 
  left 
  and 
  

   an 
  approach 
  of 
  the 
  r 
  to 
  the 
  molecular 
  diameter. 
  * 
  Temperature 
  

   decrease 
  has 
  the 
  reverse 
  effect, 
  moving 
  the 
  point 
  of 
  intersection 
  

   to 
  the 
  right. 
  It 
  is 
  then 
  merely 
  necessary 
  to 
  suppose 
  the 
  two 
  

   curves 
  to 
  have 
  very 
  nearly 
  the 
  same 
  slope 
  beyond 
  r 
  , 
  to 
  bring 
  

   about 
  an 
  enormous 
  increase 
  in 
  the 
  diameter 
  of 
  the 
  colloidal 
  

   particle 
  2r 
  m 
  for 
  very 
  slight 
  thermal 
  shifting. 
  This 
  is 
  illus- 
  

   trated 
  in 
  fig. 
  7, 
  and 
  is 
  the 
  most 
  natural 
  conception 
  I 
  can 
  form 
  

   of 
  coagulation. 
  If 
  the 
  mass 
  is 
  very 
  viscous, 
  the 
  condition 
  of 
  

   equilibrium 
  will 
  rarely 
  be 
  approached 
  but 
  very 
  slowly. 
  Sep- 
  

   arately 
  considered, 
  the 
  curves 
  assert 
  that 
  with 
  increasing 
  size 
  of 
  

  

  