﻿Mr. 
  J. 
  Rose-Innes 
  on 
  the 
  Isothermals 
  of 
  Ether. 
  103 
  

  

  experimental 
  work 
  on 
  Isopentane. 
  The 
  main 
  conclusions 
  

   arrived 
  at 
  were 
  as 
  follows 
  : 
  — 
  

  

  (i.) 
  The 
  study 
  of 
  a 
  diagram 
  constructed 
  by 
  plotting 
  

  

  — 
  2 
  against 
  v~i, 
  where 
  a 
  is 
  the 
  internal 
  pressure 
  and 
  v 
  is 
  the 
  

  

  volume 
  of 
  a 
  gram, 
  suggests 
  that 
  there 
  is 
  a 
  discontinuity 
  in 
  

  

  the 
  slope 
  of 
  — 
  %• 
  Even 
  if 
  there 
  is 
  not 
  discontinuity 
  in 
  the 
  

  

  exact 
  sense 
  of 
  the 
  word, 
  there 
  is 
  an 
  extremely 
  rapid 
  change 
  

   of 
  behaviour, 
  amounting 
  practically 
  to 
  the 
  same 
  thing. 
  

  

  (ii.) 
  The 
  temperature 
  for 
  which 
  the 
  pressure 
  is 
  accurately 
  

   given 
  by 
  the 
  laws 
  of 
  a 
  perfect 
  gas 
  at 
  a 
  given 
  volume, 
  remains 
  

   practically 
  constant 
  for 
  all 
  large 
  volumes, 
  until 
  we 
  approach 
  

   the 
  neighbourhood 
  of 
  the 
  critical 
  volume. 
  At 
  the 
  critical 
  

   volume 
  this 
  temperature 
  has 
  diminished 
  somewhat 
  from 
  its 
  

   value 
  for 
  large 
  volumes, 
  but 
  the 
  diminution 
  is 
  only 
  slight. 
  

  

  These 
  conclusions 
  were 
  embodied 
  in 
  a 
  formula 
  giving 
  the 
  

   pressure 
  in 
  terms 
  of 
  the 
  temperature 
  and 
  volume, 
  and 
  a 
  com- 
  

   parison 
  between 
  calculation 
  and 
  experiment 
  was 
  effected 
  by 
  

   means 
  of 
  a 
  diagram. 
  It 
  is 
  not 
  suggested 
  that 
  this 
  formula 
  

   is 
  incapable 
  of 
  further 
  improvement, 
  but 
  the 
  close 
  correspon- 
  

   dence 
  between 
  calculation 
  and 
  experiment 
  seems 
  to 
  show 
  that 
  

   the 
  main 
  conclusions 
  on 
  which 
  the 
  formula 
  was 
  founded 
  are 
  

   correct. 
  

  

  A 
  natural 
  extension 
  of 
  the 
  above 
  investigation 
  is 
  to 
  try 
  

   how 
  far 
  these 
  general 
  conclusions 
  are 
  true 
  of 
  some 
  other 
  

   substance. 
  Fortius 
  purpose 
  I 
  resolved 
  to 
  employ 
  the 
  experi- 
  

   mental 
  results 
  obtained 
  by 
  Profs. 
  Ramsay 
  and 
  Young 
  with 
  

   ether, 
  as 
  it 
  appears 
  that 
  the 
  linear 
  law 
  connecting 
  temperature 
  

   and 
  pressure 
  at 
  constant 
  volume 
  holds 
  accurately 
  in 
  this 
  case. 
  

   [Phil. 
  Trans, 
  vol. 
  178 
  A, 
  pp. 
  57-93 
  ; 
  and 
  Phil. 
  Mag. 
  vol.xxiii. 
  

   pp. 
  435-458.] 
  

  

  Profs. 
  Ramsay 
  and 
  Young 
  have 
  given 
  the 
  values 
  of 
  a 
  for 
  

   a 
  large 
  number 
  of 
  volumes 
  (Phil. 
  Mag. 
  vol. 
  xxiii. 
  p. 
  441), 
  

  

  so 
  that 
  it 
  was 
  easy 
  to 
  calculate 
  the 
  values 
  of 
  — 
  § 
  ? 
  auc 
  ^ 
  ^° 
  P^ 
  

  

  them 
  against 
  v~i. 
  The 
  resulting 
  diagram 
  is 
  given 
  on 
  p. 
  104, 
  

   and 
  it 
  suggests 
  very 
  strongly 
  that 
  there 
  is 
  a 
  discontinuity 
  of 
  

   slope 
  at 
  about 
  vol. 
  3'3. 
  In 
  this 
  respect, 
  accordingly, 
  the 
  

   ether 
  results 
  show 
  a 
  striking 
  likeness 
  to 
  those 
  of 
  isopentane, 
  

   the 
  discontinuity 
  in 
  the 
  case 
  of 
  the 
  last 
  substance 
  occurring 
  

   at 
  about 
  the 
  same 
  volume. 
  

  

  It 
  was 
  shown 
  in 
  my 
  former 
  paper 
  that 
  when 
  Ramsay 
  and 
  

   Young's 
  linear 
  law 
  holds, 
  there 
  is 
  one 
  and 
  only 
  one 
  tempera- 
  

   ture 
  for 
  each 
  yolume 
  at 
  which 
  the 
  pressure 
  is 
  given 
  by 
  .the 
  

  

  