﻿Pressure, 
  and 
  Latent 
  Heat 
  of 
  Vaporization. 
  393 
  

  

  " 
  constant," 
  19' 
  89. 
  Likewise 
  from 
  extrapolation 
  of 
  Cahours* 
  

   determinations 
  of 
  the 
  vapor 
  density 
  of 
  acetic 
  acid, 
  its 
  vapor 
  

   density 
  at 
  118° 
  may 
  be 
  set 
  at 
  3*3, 
  which 
  by 
  multiplication 
  by 
  

   28*87 
  gives 
  as 
  molecular 
  mass 
  95 
  ; 
  and 
  this 
  in 
  turn 
  shows 
  the 
  

   value 
  of 
  the 
  " 
  constant 
  " 
  to 
  be 
  W'Slf,. 
  Now 
  we 
  have 
  every 
  

   reason 
  to 
  believe 
  that 
  the 
  gaseous 
  associated 
  molecule 
  does 
  not 
  

   dissociate 
  on 
  passing 
  into 
  the 
  liquid 
  state 
  ; 
  on 
  the 
  contrary, 
  

   there 
  can 
  scarcely 
  be 
  any 
  doubt 
  but 
  that 
  it 
  increases 
  more 
  or 
  

   less 
  in 
  complexity. 
  Accordingly, 
  the 
  molecular 
  masses 
  calcu- 
  

   lated 
  for 
  the 
  gaseous 
  molecules 
  may 
  be 
  set 
  as 
  very 
  near 
  those 
  

   of 
  the 
  liquid 
  molecules 
  of 
  the 
  two 
  acids 
  in 
  question, 
  and, 
  

   indeed, 
  the 
  experiments 
  of 
  Schallt 
  indicate 
  that 
  for 
  acetic 
  acid, 
  

   at 
  least, 
  such 
  is 
  the 
  state 
  of 
  affairs. 
  The 
  values 
  of 
  the 
  " 
  con- 
  

   stant 
  " 
  found 
  for 
  these 
  corrected 
  molecular 
  masses 
  are 
  seen 
  to 
  

   be 
  practically 
  identical 
  with 
  that 
  found 
  for 
  normal 
  liquids, 
  and 
  

   the 
  exception 
  presented 
  by 
  the 
  acids 
  is 
  seen 
  to 
  be 
  but 
  seeming. 
  

   For 
  butyric 
  and 
  valeric 
  acids, 
  however, 
  the 
  " 
  constants 
  " 
  can- 
  

   not 
  be 
  corrected 
  as 
  for 
  the 
  two 
  preceding 
  acids, 
  since 
  they 
  are 
  

   found 
  to 
  be 
  too 
  large 
  even 
  when 
  calculated 
  on 
  the 
  assumption 
  

   that 
  their 
  molecular 
  masses 
  are 
  normal. 
  If 
  their 
  determina- 
  

   tions 
  of 
  latent 
  heat 
  of 
  volatilization 
  are 
  sufficiently 
  accurate 
  — 
  

   which 
  is 
  somewhat 
  doubtful 
  — 
  it 
  is 
  probable 
  that 
  the 
  complex 
  

   liquid 
  molecules 
  in 
  their 
  case 
  undergo 
  decomposition 
  on 
  pass- 
  

   ing 
  into 
  the 
  vaporous 
  state, 
  similar 
  to 
  the 
  alcohols, 
  etc. 
  In 
  

   the 
  absence 
  of 
  experiments 
  on 
  their 
  vapor 
  densities 
  it 
  is 
  not 
  

   possible 
  to 
  judge 
  what 
  is 
  the 
  true 
  state 
  of 
  the 
  case. 
  

  

  Nitromethane 
  and 
  nitroethane 
  also 
  give 
  values 
  of 
  the 
  con- 
  

   stant 
  less 
  than 
  the 
  normal. 
  Ramsay 
  and 
  Shields^ 
  have 
  meas- 
  

   ured 
  the 
  superficial 
  tension 
  of 
  nitroethane, 
  finding 
  it 
  such 
  as 
  

   to 
  legitimatize 
  the 
  assumption 
  that 
  the 
  molecules 
  of 
  this 
  liquid 
  

   are 
  in 
  a 
  state 
  of 
  association 
  ; 
  by 
  analogy 
  it 
  may 
  be 
  admitted 
  

   that 
  nitromethane 
  is 
  also 
  an 
  associated 
  liquid, 
  although 
  no 
  

   experimental 
  data 
  are 
  at 
  hand. 
  If 
  what 
  has 
  been 
  said 
  in 
  

   explanation 
  of 
  the 
  seeming 
  abnormality 
  in 
  the 
  behavior 
  of 
  the 
  

   acids 
  as 
  regards 
  the 
  u 
  constant 
  " 
  be 
  in 
  accordance 
  with 
  fact, 
  it 
  

   is 
  necessary 
  to 
  suppose 
  that 
  the 
  two 
  nitro-compounds 
  also 
  pass 
  

   from 
  the 
  liquid 
  into 
  the 
  gaseous 
  condition 
  without 
  the 
  com- 
  

   plex 
  molecule 
  suffering 
  much 
  dissociation. 
  

  

  The 
  immediately 
  preceding 
  considerations 
  indicate 
  a 
  method 
  

   of 
  getting 
  an 
  approximation 
  of 
  the 
  degree 
  of 
  association 
  of 
  a 
  

   liquid. 
  If 
  any 
  liquid, 
  whose 
  latent 
  heat 
  of 
  volatilization 
  be 
  

   known, 
  gives 
  a 
  value 
  for 
  the 
  " 
  constant 
  " 
  close 
  to 
  20*7, 
  it 
  is 
  

   pretty 
  certain 
  that 
  it 
  is 
  normal. 
  v 
  If 
  it 
  gives 
  a 
  less 
  value, 
  it 
  is 
  

   associated 
  in 
  the 
  liquid 
  as 
  well 
  as 
  in 
  the 
  gaseous 
  state 
  ; 
  if 
  it 
  

  

  * 
  Comp. 
  Rend., 
  xix, 
  771. 
  

  

  f 
  Ber. 
  der 
  deutschen 
  chem. 
  Gesell., 
  xvii, 
  2199, 
  1884. 
  

   % 
  Zeitschr. 
  fur 
  phys. 
  Chem., 
  xii, 
  433, 
  1893. 
  

   Am. 
  Jour. 
  Sci.— 
  Third 
  Series, 
  Yol. 
  XLIX, 
  No 
  293.— 
  May, 
  1895. 
  

   26 
  

  

  