﻿■308 
  Dr. 
  Donnan 
  on 
  Condensation 
  of 
  the 
  Vapours 
  of 
  

  

  made 
  for 
  the 
  pressure 
  of 
  the 
  saturated 
  vapour 
  at 
  the 
  tempera- 
  

   ture 
  of 
  the 
  experiment, 
  gives 
  the 
  volume-expansion 
  ratio. 
  

   An 
  etched 
  scale 
  on 
  b 
  enables 
  one 
  to 
  repeat 
  any 
  given 
  ex- 
  

   pansion 
  as 
  often 
  as 
  necessary, 
  and 
  serves 
  as 
  a 
  fiducial 
  scale 
  

   generally. 
  A 
  layer 
  of 
  mercury 
  protects 
  the 
  rubber 
  stopper 
  

   (r) 
  from 
  the 
  action 
  of 
  the 
  liquid 
  in 
  i. 
  The 
  wired 
  rubber 
  

   connexion 
  (s) 
  enables 
  the 
  cloud-vessel 
  to 
  be 
  readily 
  detached 
  

   and 
  cleaned. 
  The 
  experiments 
  were 
  made 
  in 
  a 
  dark 
  room, 
  

   and 
  the 
  cloud-vessel 
  (i) 
  was 
  illuminated 
  as 
  recommended 
  by 
  

   Wilson*. 
  

  

  § 
  3. 
  Liquids 
  used. 
  

  

  Water. 
  — 
  Ordinary 
  distilled 
  water. 
  

  

  Ethyl 
  alcohol. 
  — 
  Dried 
  by 
  lime 
  first, 
  and 
  then 
  by 
  repeated 
  

   distillation 
  from 
  small 
  quantities 
  of 
  sodium. 
  B.-Pt. 
  constant. 
  

  

  Methyl 
  alcohol. 
  — 
  Similarly 
  treated. 
  (Kahlbaum's 
  best 
  

   quality.) 
  

  

  Benzene, 
  Chlorobenzene, 
  Carbon 
  tetrachloride. 
  Carbon 
  disid- 
  

   phide. 
  — 
  From 
  Kahlbaum. 
  They 
  were 
  dried 
  by 
  P 
  2 
  5 
  , 
  and 
  

   fractionated 
  to 
  constant 
  B.-Pt. 
  These 
  B.-Pt.'s 
  agreed 
  with 
  

   the 
  values 
  taken 
  by 
  interpolation 
  from 
  Ramsay 
  and 
  Young's 
  

   results 
  for 
  the 
  corresponding 
  pressures. 
  The 
  carbon 
  disul- 
  

   phide 
  was 
  purified 
  by 
  shaking 
  with 
  mercury 
  before 
  distillation. 
  

  

  The 
  data 
  as 
  regards 
  the 
  vapour-pressures 
  of 
  the 
  organic- 
  

   liquids 
  employed 
  were 
  obtained 
  by 
  calculation 
  from 
  Ramsay 
  

   and 
  Young's 
  results. 
  

  

  § 
  4. 
  Results. 
  

  

  Substance. 
  

  

  Rain-point 
  

   Expansion. 
  

  

  Fog-point 
  

   Expansion. 
  

  

  Temperature 
  of 
  

   Experiments. 
  

  

  Water 
  

  

  1-29 
  

  

  1-32 
  

   1-20 
  

   1-89 
  

   1-05 
  

   148 
  

   1-53 
  

  

  1-42 
  

   1-42 
  

   1-25 
  

  

  Not 
  observed. 
  

   1-08 
  

   1-60 
  

   1-78 
  

  

  20-5-20-8 
  

  

  16-8 
  

   17-2-17-5 
  

  

  16-5 
  

  

  16-5 
  

  

  16-3 
  

   18-18-5 
  

  

  Methyl 
  alcohol 
  

  

  Ethyl 
  alcohol 
  

  

  Carbon 
  tetrachloride 
  ... 
  

  

  Carbon 
  disulphide 
  

  

  Chlorobenzene 
  

  

  

  

  

  

  The 
  results 
  for 
  water 
  are 
  not 
  quite 
  the 
  same 
  as 
  the 
  values 
  

   given 
  by 
  Wilson 
  ; 
  but, 
  as 
  Wilson 
  has 
  pointed 
  out 
  himself, 
  the 
  

   values 
  obtained 
  depend 
  somewhat 
  on 
  the 
  form 
  of 
  apparatus 
  

   used. 
  Doubtless 
  in 
  the 
  present 
  case 
  the 
  connecting 
  neck 
  

   between 
  the 
  cloud-vessel 
  and 
  the 
  expansion-cylinder 
  would 
  

   tend 
  to 
  make 
  the 
  measured 
  expansion 
  greater 
  than 
  the 
  

  

  * 
  For 
  the 
  methods 
  of 
  obtaining 
  dust-free 
  air 
  and 
  other 
  particulars 
  of 
  

   manipulation, 
  reference 
  must 
  be 
  made 
  to 
  Wilson's 
  papers. 
  

  

  