﻿relation 
  to 
  Pressure 
  and 
  Temperature* 
  223 
  

  

  all 
  the 
  normal 
  substances 
  examined 
  with 
  a 
  close 
  approach 
  

   to 
  accuracy, 
  yet 
  the 
  deviations 
  are 
  too 
  regular 
  to 
  be 
  ascribed 
  

   to 
  experimental 
  error. 
  The 
  relation 
  between 
  the 
  mean 
  

   densities 
  of 
  liquid 
  and 
  saturated 
  vapour 
  and 
  the 
  temperature 
  

   is 
  represented 
  with 
  great 
  accuracy 
  by 
  the 
  formula 
  

  

  where 
  a 
  is 
  always 
  negative 
  and 
  j3 
  may 
  be 
  either 
  positive 
  or 
  

   negative. 
  The 
  direction 
  and 
  extent 
  of 
  the 
  curvature 
  of 
  the 
  

   diameter 
  is 
  indicated 
  by 
  the 
  sign 
  and 
  magnitude 
  o£ 
  the 
  

   constant 
  j3. 
  

  

  The 
  close 
  connexion 
  between 
  Mr. 
  Haigh's 
  dual 
  equation 
  

   and 
  the 
  law 
  o£ 
  Cailletet 
  and 
  Mathias 
  is 
  shown 
  by 
  the 
  fol- 
  

   lowing 
  table 
  in 
  which 
  the 
  normal 
  substances, 
  excluding 
  

   carbon 
  tetrachloride 
  and 
  stannic 
  chloride, 
  are 
  arranged 
  in 
  

  

  

  Mean 
  value 
  

   of 
  2. 
  

  

  /3xl0 
  10 
  . 
  

  

  

  1603 
  

  

  16-03 
  

  

  16-02 
  

  

  15-986 
  

  

  15-98 
  

  

  15-95 
  

  

  15'95 
  

  

  15-89 
  

  

  15-82 
  

  

  15-76 
  

  

  1593 
  

   15 
  75 
  

  

  4- 
  791 
  

   + 
  413 
  

   4- 
  693 
  

   4- 
  463 
  

   4- 
  293 
  

   

   

  

  - 
  475 
  

  

  - 
  592 
  

   -1046 
  

  

  +1480 
  

  

  4- 
  977 
  

  

  Di-isopropyl 
  

  

  

  Isopentane 
  

  

  Fluorbenzene 
  

  

  

  w-Hexane 
  

  

  Ether 
  

  

  Di-isobutyl 
  

  

  w-Octane 
  

  

  Carbon 
  tetrachloride 
  

  

  Stannic 
  chloride 
  

  

  

  order 
  of 
  magnitude 
  of 
  the 
  mean 
  values 
  of 
  2. 
  It 
  will 
  be 
  

   seen 
  that 
  with 
  one 
  exception 
  the 
  values 
  of 
  /3 
  x 
  10 
  10 
  follow 
  

   the 
  same 
  order, 
  2 
  falling 
  from 
  16-03 
  to 
  15*76 
  while 
  8xl0 
  10 
  

   changes 
  from 
  + 
  791 
  to 
  — 
  1046. 
  The 
  one 
  deviation, 
  that 
  

   shown 
  by 
  di-isopropyl, 
  is 
  small 
  ; 
  and 
  it 
  is 
  probable 
  that 
  the 
  

   mean 
  value 
  of 
  2 
  for 
  n-pentane 
  should 
  be 
  slightly 
  higher 
  

   and 
  of 
  ?i-hexane 
  slightly 
  lower 
  than 
  15*95, 
  and 
  that 
  /Sx 
  10 
  10 
  

   for 
  the 
  latter 
  substance 
  should 
  have 
  a 
  small 
  negative 
  value. 
  

  

  The 
  connexion 
  seems 
  to 
  break 
  down 
  altogether 
  when 
  the 
  

   two 
  chlorides 
  are 
  compared 
  with 
  the 
  other 
  substances, 
  but 
  it 
  

   is 
  possible 
  that 
  a 
  considerable 
  part 
  of 
  the 
  discrepancy 
  may 
  

   be 
  explained 
  by 
  the 
  relatively 
  large 
  experimental 
  errors 
  to 
  

   which 
  reference 
  has 
  been 
  made. 
  

  

  