﻿Properties 
  of 
  Carbon 
  Dioxide 
  and 
  of 
  Ethane. 
  629 
  

  

  the 
  lowest 
  temperature, 
  and 
  is 
  of 
  opposite 
  sign 
  to 
  the 
  deviations 
  

   for 
  abnormal 
  associating 
  substances. 
  We 
  cannot 
  say 
  with 
  

   certainty 
  whether 
  these 
  deviations 
  are 
  characteristic 
  of 
  pure 
  

   ethane. 
  The 
  ethane, 
  although 
  submitted 
  to 
  repeated 
  frac- 
  

   tional 
  distillation, 
  was 
  not 
  so 
  pure 
  as 
  the 
  carbon 
  dioxide 
  ; 
  

   and 
  it 
  is 
  quite 
  possible 
  that 
  the 
  deviations 
  in 
  question 
  are 
  to 
  

   be 
  accounted 
  for 
  by 
  the 
  presence 
  of 
  impurity. 
  At 
  the 
  tem- 
  

   peratures 
  above 
  0° 
  C. 
  the 
  whole 
  mass 
  of 
  the 
  substance 
  was 
  

   immersed 
  in 
  the 
  temperature-bath, 
  but 
  below 
  0° 
  C. 
  an 
  ap- 
  

   proximately 
  constant 
  part 
  of 
  the 
  tube 
  was 
  cooled 
  in 
  the 
  Dewar 
  

   vessel. 
  Because 
  of 
  this 
  complexity 
  in 
  the 
  experimental 
  con- 
  

   ditions, 
  it 
  is 
  impossible 
  to 
  account 
  for 
  the 
  above 
  differences 
  in 
  

   detail, 
  or 
  to 
  estimate 
  the 
  actual 
  error 
  which 
  the 
  impurity 
  

   must 
  have 
  produced 
  at 
  the 
  various 
  temperatures, 
  if 
  we 
  assume 
  

   them 
  to 
  be 
  due 
  to 
  that 
  cause. 
  

  

  We 
  have 
  no 
  data 
  for 
  the 
  liquid 
  and 
  vapour 
  densities 
  of 
  

   ethane 
  sufficiently 
  accurate 
  to 
  test 
  the 
  diameter 
  law, 
  and 
  to 
  

   find 
  by 
  extrapolation 
  the 
  densities 
  at 
  the 
  lower 
  temperatures 
  

   which 
  are 
  required 
  for 
  the 
  calculation 
  of 
  the 
  latent 
  heat. 
  

  

  The 
  critical 
  volume 
  as 
  determined 
  directly 
  by 
  experiment 
  

   was 
  *0O65 
  of 
  the 
  gas 
  volume 
  at 
  0° 
  C. 
  and 
  one 
  atmosphere. 
  

   From 
  this 
  we 
  calculate 
  for 
  the 
  critical 
  volume 
  4*84 
  c.c. 
  

   per 
  gram. 
  The 
  ratio 
  of 
  the 
  critical 
  density 
  to 
  the 
  density 
  

   calculated 
  by 
  the 
  gaseous 
  laws 
  we 
  find 
  to 
  be 
  3*55. 
  The 
  

   uncertainty 
  of 
  these 
  figures 
  we 
  estimate 
  at 
  about 
  2 
  per 
  cent. 
  

   If 
  we 
  consult 
  Young's 
  tables 
  referred 
  to 
  before 
  "*, 
  we 
  find 
  that, 
  

   judging 
  by 
  the 
  position 
  which 
  the 
  other 
  normal 
  hydrocarbons 
  

   take 
  up 
  in 
  it, 
  the 
  ratio 
  for 
  ethane 
  should 
  be 
  less 
  than 
  for 
  

   pentane, 
  3*765, 
  as 
  is 
  actually 
  the 
  case. 
  The 
  ratios 
  for 
  propane 
  

   and 
  butane 
  are 
  not 
  yet 
  accurately 
  known 
  ; 
  but 
  those 
  for 
  

   hexane, 
  heptane, 
  &c. 
  increase 
  regularly 
  the 
  higher 
  we 
  go 
  up 
  

   the 
  series. 
  

  

  In 
  order 
  to 
  obtain 
  approximate 
  values 
  for 
  the 
  latent 
  heat 
  

   of 
  evaporation 
  of 
  ethane, 
  we 
  have 
  assumed 
  that 
  the 
  corre- 
  

   sponding 
  volumes 
  of 
  vapour 
  and 
  liquid 
  are 
  the 
  same 
  as 
  

   for 
  carbon 
  tetrachloride, 
  considering 
  that 
  this 
  substance 
  

   resembles 
  ethane 
  more 
  than 
  any 
  other 
  contained 
  in 
  Young's 
  

   tables. 
  

  

  In 
  comparing 
  the 
  volumes 
  thus 
  obtained 
  with 
  the 
  volumes 
  

   calculated 
  by 
  the 
  gaseous 
  laws, 
  we 
  find 
  the 
  latter 
  slightly 
  

   larger, 
  as 
  they 
  should 
  be, 
  with 
  the 
  exception 
  of 
  the 
  volume 
  

   at 
  the 
  lowest 
  temperature 
  — 
  74°* 
  7, 
  the 
  volumes 
  being 
  253 
  

   and 
  256. 
  The 
  latter 
  number 
  is 
  thus 
  seen 
  to 
  be 
  a 
  few 
  per 
  cent, 
  

   too 
  large. 
  

  

  * 
  Young, 
  Phil. 
  Mag. 
  [5] 
  1. 
  p. 
  296. 
  

  

  