﻿Pressure, 
  and 
  Latent 
  Heat 
  of 
  Vaporization. 
  383 
  

  

  tially 
  independent 
  expressions 
  tie 
  makes 
  two 
  hypotheses 
  : 
  1, 
  

   the 
  cohesion 
  of 
  liquids 
  is 
  the 
  same 
  for 
  all 
  : 
  2, 
  Carnot's 
  cycle 
  is 
  

   applicable 
  to 
  volatile 
  liquids, 
  and 
  to 
  their 
  changes 
  of 
  volume 
  : 
  

   and 
  there 
  exists 
  a 
  relation 
  between 
  heat 
  taken 
  in 
  and 
  work 
  

   performed. 
  The 
  expressions 
  finally 
  arrived 
  at 
  show 
  a 
  satisfac- 
  

   tory 
  correspondence 
  for 
  the 
  most 
  part 
  with 
  the 
  determinations 
  

   of 
  latent 
  heats 
  of 
  vaporization 
  made 
  by 
  Regnault. 
  The 
  con- 
  

   clusions 
  which 
  have 
  a 
  bearing 
  upon 
  our 
  subject 
  are 
  : 
  I 
  — 
  The 
  

   product 
  of 
  the 
  latent 
  heats 
  of 
  liquids 
  at 
  the 
  same 
  pressure 
  by 
  

   their 
  atomic 
  weights, 
  divided 
  by 
  the 
  absolute 
  temperature 
  at 
  

   which 
  the 
  vaporization 
  takes 
  place, 
  is 
  the 
  same 
  for 
  all 
  : 
  II 
  — 
  

   The 
  difference 
  between 
  the 
  internal 
  heats 
  of 
  vaporization 
  at 
  

   any 
  two 
  temperatures, 
  multiplied 
  by 
  the 
  atomic 
  weights, 
  is 
  a 
  

   constant 
  number 
  for 
  all 
  liquids. 
  

  

  We 
  will 
  not 
  enter 
  into 
  any 
  discussion 
  of 
  these 
  results, 
  con- 
  

   tenting 
  ourselves 
  with 
  remarking 
  that 
  the 
  first 
  conclusion 
  is 
  a 
  

   plain 
  enunciation 
  of 
  " 
  Trouton's 
  law 
  " 
  mentioned 
  above. 
  If 
  

   priority 
  of 
  publication 
  has 
  any 
  moment 
  in 
  the 
  choice 
  of 
  the 
  

   name 
  of 
  a 
  discovery, 
  the 
  law 
  in 
  question 
  ought 
  to 
  be 
  called 
  

   Pictet's 
  law 
  since 
  the 
  date 
  of 
  Pictet's 
  paper 
  is 
  1876 
  and 
  that 
  of 
  

   Trouton's 
  1884. 
  

  

  Equation 
  (1) 
  seems 
  first 
  to 
  have 
  been 
  made 
  use 
  of 
  by 
  van 
  

   der 
  Waals- 
  for 
  the 
  establishing 
  of 
  relationships 
  between 
  tem- 
  

   perature, 
  pressure, 
  and 
  latent 
  heat 
  of 
  evaporation. 
  If 
  for 
  p, 
  

  

  T, 
  and 
  v, 
  ej>, 
  m 
  T 
  v 
  and 
  <p(m)— 
  (j? 
  x 
  being 
  the 
  critical 
  pressure, 
  

  

  T 
  : 
  , 
  the 
  critical 
  temperature, 
  b, 
  the 
  covolume, 
  and 
  e, 
  m, 
  <p(m), 
  

   coefficients) 
  be 
  substituted 
  in 
  equation 
  (1), 
  and 
  it 
  be 
  kept 
  in 
  

   mind 
  that 
  

  

  — 
  =/(ro), 
  

  

  (u 
  being 
  the 
  molecular 
  mass), 
  the 
  equation 
  

   de 
  _ 
  8-273 
  pu, 
  1 
  

   dm 
  ~ 
  A 
  ' 
  T 
  ' 
  cpm 
  ^ 
  ' 
  

  

  ^- 
  c 
  -^f-~ 
  w 
  

  

  or 
  

  

  de 
  _ 
  n 
  pfi 
  l_ 
  

  

  results. 
  ]STow 
  when 
  m 
  is 
  the 
  same, 
  that 
  is, 
  at 
  the 
  same 
  reduced 
  

  

  de 
  

   temperature, 
  — 
  must 
  have 
  the 
  same 
  value, 
  and 
  as 
  a 
  necessary 
  

  

  consequence 
  it 
  follows 
  that 
  

  

  §£ 
  = 
  F(m) 
  (5) 
  

  

  * 
  Continuitat 
  des 
  gasformigen 
  und 
  flussigen 
  Zustandes, 
  p. 
  137. 
  

  

  