﻿Pressure, 
  and 
  Latent 
  Heat 
  of 
  Vaporization. 
  381 
  

  

  differential 
  forms 
  of 
  equations 
  (1) 
  and 
  (2) 
  do 
  not 
  readily 
  permit 
  

   of 
  direct 
  comparison 
  with 
  empirical 
  facts 
  ; 
  they 
  must 
  first 
  by 
  

   suitable 
  hypotheses 
  and 
  integrations 
  be 
  thrown 
  into 
  other 
  forms. 
  

   The 
  comparison 
  of 
  the 
  deductions 
  and 
  discovered 
  relationships 
  

   with 
  the 
  experimental 
  data 
  generally 
  shows 
  a 
  close 
  correspond- 
  

   ence. 
  Sometimes, 
  however, 
  variations 
  and 
  exceptions 
  occur 
  

   which 
  cannot 
  be 
  referred 
  to 
  experimental 
  errors. 
  

  

  The 
  object 
  of 
  this 
  paper 
  is 
  to 
  give 
  an 
  account 
  of 
  the 
  efforts 
  

   that 
  have 
  been 
  made 
  and 
  the 
  results 
  that 
  have 
  been 
  obtained 
  

   in 
  regard 
  to 
  the 
  relations 
  between 
  pressure, 
  temperature, 
  and 
  

   latent 
  heat 
  of 
  vaporization 
  ; 
  to 
  subject 
  to 
  a 
  critical 
  revision 
  all 
  

   experimental 
  data 
  bearing 
  upon 
  the 
  question 
  ; 
  to 
  discuss 
  the 
  

   differences 
  seemingly 
  present 
  between 
  theory 
  and 
  experiment 
  ; 
  

   and 
  to 
  apply 
  the 
  results 
  to 
  certain 
  practical 
  problems. 
  The 
  

   division 
  of 
  the 
  matter 
  is 
  the 
  following: 
  first, 
  a 
  historical 
  

   account 
  of 
  such 
  papers 
  as 
  have 
  dealt 
  with 
  the 
  theoretical 
  side 
  

   of 
  the 
  question 
  ; 
  second, 
  a 
  review 
  in 
  tabular 
  form 
  of 
  experi- 
  

   mental 
  data 
  together 
  with 
  a 
  discussion 
  of 
  their 
  comparative 
  

   value 
  ; 
  third, 
  a 
  comparison 
  of 
  the 
  results 
  of 
  theory 
  and 
  experi- 
  

   ment; 
  fourth, 
  an 
  application 
  of 
  results 
  to 
  a 
  practical 
  problem. 
  

  

  I. 
  

  

  The 
  first 
  paper 
  in 
  which 
  an 
  endeavor 
  was 
  made 
  to 
  find 
  out 
  

   relations 
  between 
  latent 
  heats 
  of 
  vaporization 
  and 
  other 
  energy- 
  

   factors 
  is 
  due 
  to 
  ITre;"* 
  this 
  pioneer 
  in 
  this 
  field 
  of 
  research 
  

   determined 
  the 
  heats 
  of 
  vaporization 
  of 
  a 
  number 
  of 
  common 
  

   liquids, 
  and 
  concluded 
  from 
  his 
  results 
  that 
  under 
  the 
  same 
  

   pressure 
  the 
  latent 
  heat 
  of 
  vaporization 
  is 
  inversely 
  propor- 
  

   tional 
  to 
  the 
  vapor 
  density. 
  

  

  Desprets,f 
  in 
  a 
  paper 
  read 
  before 
  the 
  French 
  Academy 
  

   towards 
  the 
  end 
  of 
  the 
  year 
  1818, 
  but 
  of 
  which 
  merely 
  an 
  

   abstract 
  seems 
  ever 
  to 
  have 
  been 
  published, 
  communicated 
  the 
  

   results 
  of 
  some 
  determinations 
  of 
  the 
  latent 
  heats 
  of 
  vaporiza- 
  

   tion 
  of 
  water, 
  alcohol, 
  ether, 
  and 
  essence 
  of 
  terebinthine. 
  

   An 
  inspection 
  of 
  his 
  data 
  led 
  him 
  to 
  state 
  that 
  a 
  liquid 
  at 
  its 
  

   point 
  of 
  ebullition 
  requires 
  for 
  volatilization 
  so 
  much 
  the 
  less 
  

   heat, 
  the 
  denser 
  its 
  vapor 
  ; 
  latent 
  heats 
  of 
  vaporization 
  are 
  

   approximately 
  proportional 
  to 
  densities 
  at 
  the 
  boiling 
  points. 
  

  

  Person;}: 
  after 
  determining 
  the 
  latent 
  heats 
  of 
  vaporization 
  

   of 
  ten 
  additional 
  liquids, 
  notwithstanding 
  that 
  his 
  results 
  were 
  

   not 
  as 
  accurate 
  as 
  those 
  of 
  Desprets, 
  as 
  he 
  himself 
  admits, 
  and 
  

   without 
  giving 
  any 
  data, 
  formulated 
  a 
  law, 
  which 
  is 
  u 
  for 
  the 
  

   heat 
  of 
  vaporization 
  what 
  the 
  law 
  'of 
  Dulong 
  and 
  Petit 
  is 
  for 
  

   the 
  specific 
  heat," 
  and 
  " 
  even 
  more 
  general, 
  since 
  it 
  applies 
  to 
  

  

  *Phil. 
  Mag. 
  liii, 
  191, 
  1819. 
  

  

  f 
  Ann. 
  Chim. 
  et 
  Phys., 
  xxiv, 
  323, 
  1823. 
  

  

  % 
  Comptes 
  Rend., 
  xvii, 
  498, 
  1843. 
  

  

  