﻿in 
  Their 
  Thermodynamic 
  Relations. 
  173 
  

  

  particle 
  or 
  number 
  of 
  molecules 
  to 
  the 
  aggregate, 
  the 
  attractions 
  

   of 
  particles 
  for 
  each 
  other 
  and 
  for 
  the 
  liquid 
  decrease. 
  The 
  

   nature 
  of 
  these 
  forces 
  is 
  thus 
  a 
  residual 
  affinity. 
  

  

  12. 
  If 
  again 
  we 
  turn 
  to 
  the 
  chart, 
  fig. 
  

  

  4, 
  and 
  inquire 
  what 
  will 
  be 
  the 
  shape 
  ^ 
  

   of 
  the 
  isotherm 
  in 
  a 
  pv 
  diagram, 
  we 
  

   observe 
  that 
  the 
  reaction 
  begins 
  with 
  

   the 
  small 
  compressibilities 
  (large 
  bulk 
  

   modulus) 
  of 
  pure 
  water, 
  then 
  passes 
  

   through 
  enormous 
  values 
  of 
  compressi- 
  

   bility 
  back 
  again 
  to 
  the 
  extremely 
  small 
  

   values 
  of 
  compressibity 
  at 
  the 
  end 
  of 
  

   the 
  reaction. 
  The 
  isothermal 
  is 
  there- 
  

   fore 
  a 
  doubly 
  inflected 
  curve 
  of 
  the 
  

   form, 
  fig. 
  8, 
  well 
  known 
  in 
  the 
  treatment 
  of 
  vapors. 
  To 
  every 
  

   point 
  of 
  the 
  present 
  curve, 
  however, 
  there 
  corresponds 
  a 
  definite 
  

   concentration 
  of 
  water 
  glass, 
  increasing 
  from 
  right 
  to 
  left. 
  

   The 
  curve 
  begins 
  with 
  compositions 
  of 
  much 
  water 
  and 
  little 
  

   glass, 
  with 
  stable 
  solutions 
  and 
  elastic 
  fluids; 
  whatever 
  water 
  

   is 
  forced 
  into 
  the 
  glass 
  corpuscles 
  by 
  pressure, 
  comes 
  freely 
  

   and 
  almost 
  wholly 
  out 
  again 
  when 
  pressure 
  is 
  relieved. 
  The 
  

   curve 
  terminates 
  in 
  compositions 
  of 
  much 
  glass 
  and 
  little 
  

   water, 
  again 
  stable 
  and 
  elastic 
  ; 
  the 
  intermediate 
  field, 
  «, 
  being 
  

   unstable 
  and 
  inelastic 
  (non-resilient). 
  In 
  view 
  of 
  the 
  exceed- 
  

   ingly 
  viscous 
  liquids 
  involved, 
  the 
  reactions 
  are 
  not 
  implosive 
  

   but 
  can 
  be 
  observed 
  through, 
  from 
  liquid 
  water 
  to 
  semi-solid 
  

   water 
  glass, 
  including 
  the 
  unstable 
  part 
  of 
  the 
  curve. 
  Looking 
  

   at 
  these 
  reactions 
  from 
  another 
  point 
  of 
  view, 
  they 
  present 
  a 
  

   striking 
  analogy 
  to 
  mass 
  action 
  in 
  which 
  either 
  the 
  water 
  or 
  

   the 
  water 
  glass 
  is 
  stable 
  according 
  as 
  an 
  excess 
  of 
  one 
  or 
  the 
  

   other 
  of 
  the 
  ingredients, 
  water 
  and 
  glass, 
  is 
  encountered. 
  The 
  

   same 
  inference 
  follows 
  from 
  the 
  experiments 
  (§ 
  3) 
  made 
  in 
  

   steel 
  retorts. 
  We 
  have 
  therefore 
  traced 
  a 
  peculiar 
  case 
  of 
  

   mass 
  action 
  evidenced 
  by 
  the 
  successive 
  values 
  of 
  the 
  com- 
  

   pressibility 
  of 
  the 
  solution. 
  

  

  13. 
  In 
  the 
  above 
  paragraphs, 
  I 
  have 
  endeavored 
  to 
  show 
  that 
  

   while 
  glass 
  expands 
  in 
  absorbing 
  water, 
  the 
  system 
  glass-water 
  

   contracts 
  20 
  per 
  cent 
  to 
  30 
  per 
  cent, 
  so 
  far 
  as 
  can 
  be 
  discerned. 
  

   The 
  important 
  question 
  thus 
  at 
  once 
  arises, 
  whether 
  so 
  large 
  a 
  

   contraction 
  as 
  this 
  can 
  be 
  supposed 
  to 
  occur 
  without 
  the 
  

   evolution 
  of 
  heat. 
  It 
  seems 
  to 
  me 
  that 
  this 
  is 
  quite 
  improba- 
  

   ble, 
  although 
  I 
  have 
  not 
  been 
  able, 
  after 
  some 
  pains, 
  to 
  com- 
  

   plete 
  a 
  direct 
  test 
  in 
  answer 
  to 
  the 
  inquiry. 
  Under 
  high 
  pressure 
  

   conditions 
  such 
  experiments 
  are 
  so 
  difficult, 
  however, 
  that 
  the 
  

   failure 
  to 
  obtain 
  direct 
  results 
  is 
  not 
  surprising 
  : 
  for 
  in 
  view 
  of 
  

   the 
  necessarily 
  small 
  lateral 
  dimensions 
  of 
  high 
  pressure 
  appa- 
  

   ratus, 
  and 
  the 
  relatively 
  slow 
  reaction, 
  etc., 
  the 
  investigation 
  of 
  

  

  