﻿Pressure, 
  and 
  Latent 
  Heat 
  of 
  Vaporization. 
  391 
  

  

  " 
  constant 
  " 
  is 
  remarkably 
  constant. 
  SchifFs 
  work 
  was 
  most 
  

   carefully 
  done 
  by 
  the 
  same 
  method 
  and 
  hence 
  his 
  results 
  are 
  at 
  

   once 
  reliable 
  and 
  comparable 
  in 
  an 
  eminent 
  degree 
  ; 
  and, 
  as 
  a 
  

   matter 
  of 
  fact, 
  the 
  extreme 
  values 
  of 
  the 
  constant 
  calculated 
  

   from 
  his 
  data 
  differ 
  from 
  the 
  average 
  value 
  by 
  hardly 
  three 
  

   per 
  cent. 
  

  

  Such 
  a 
  regularity 
  as 
  the 
  above 
  implies 
  that 
  the 
  liquids 
  at 
  

   their 
  boiling 
  points 
  are 
  in 
  corresponding 
  states 
  (the 
  term 
  " 
  cor- 
  

   responding 
  states 
  " 
  being 
  used 
  in 
  the 
  sense 
  given 
  it 
  by 
  van 
  der 
  

   Waals 
  (loc. 
  cit.) 
  As 
  far 
  as 
  the 
  pressure 
  is 
  concerned, 
  it 
  may 
  

   be 
  stated 
  that 
  atmospheric 
  pressure 
  can 
  be 
  reckoned 
  as 
  " 
  corre- 
  

   sponding 
  " 
  in 
  questions 
  of 
  this 
  sort. 
  That 
  boiling 
  points 
  for 
  

   certain 
  properties 
  of 
  liquids 
  are 
  " 
  corresponding 
  temperatures 
  " 
  

   in 
  a 
  not 
  inconsiderable 
  measure 
  has 
  been 
  shown 
  by 
  C. 
  M. 
  

   Guldberg* 
  who 
  in 
  comparing 
  the 
  quotient 
  of 
  the 
  absolute 
  

   boiling 
  points 
  by 
  the 
  absolute 
  critical 
  temperature 
  found 
  it 
  to 
  

   remain 
  close 
  to 
  an 
  average 
  value 
  of 
  about 
  f, 
  and 
  concluded 
  

   that 
  quantities 
  which 
  vary 
  slowly 
  with 
  the 
  temperature 
  (among 
  

   which 
  latent 
  heats 
  of 
  vaporization 
  are 
  to 
  be 
  counted) 
  may 
  be 
  

   reckoned 
  as 
  being 
  approximately 
  in 
  corresponding 
  states 
  at 
  

   their 
  points 
  of 
  ebullition. 
  This 
  conclusion 
  follows 
  directly 
  

   from 
  equation 
  (4) 
  which 
  indicates 
  that 
  the 
  relation 
  

  

  pu 
  , 
  T 
  

  

  -^ 
  = 
  ^T7 
  (19) 
  

  

  must 
  obtain 
  (<p 
  being 
  an 
  unknown 
  function). 
  Guldberg 
  then 
  

   states 
  that 
  through 
  comparison 
  of 
  various 
  liquids 
  the 
  equation 
  

  

  HI) 
  = 
  H 
  (20) 
  

  

  is 
  found 
  by 
  means 
  of 
  graphic 
  interpolation, 
  and 
  accordingly 
  at 
  

   the 
  boiling 
  points 
  the 
  relation 
  

  

  f=14 
  (21) 
  

  

  1 
  

  

  obtains 
  with 
  a 
  certain 
  approximation. 
  Inasmuch 
  as 
  

  

  l 
  

  

  it 
  follows 
  that 
  

  

  ^=21. 
  (22) 
  

  

  Guldberg 
  thus 
  obtains 
  about 
  the 
  same 
  " 
  constant 
  " 
  as 
  has 
  been 
  

   shown 
  in 
  the 
  foregoing 
  to 
  be 
  the 
  average 
  of 
  reliable 
  determi- 
  

   nations. 
  

  

  As 
  stated 
  above, 
  the 
  values 
  of 
  ~- 
  given 
  in 
  the 
  table 
  differ 
  

  

  *Zeitschr. 
  fur 
  phys. 
  Chemie, 
  v, 
  p. 
  374, 
  1890. 
  

  

  