﻿158 
  Dr. 
  B. 
  A. 
  Lehfeldt 
  on 
  a 
  

  

  ■could 
  not 
  obtain 
  this 
  substance, 
  even 
  after 
  repeated 
  attempts 
  

   at 
  purification, 
  in 
  the 
  same 
  condition 
  of 
  purity 
  as 
  the 
  carbon 
  

   dioxide. 
  The 
  observations 
  showed 
  this 
  distinctly. 
  The 
  

   change 
  of 
  pressure 
  with 
  change 
  of 
  volume 
  was 
  for 
  one 
  sample 
  

   from 
  23*61 
  to 
  23*97 
  atmos. 
  at 
  0°C, 
  and 
  for 
  a 
  second 
  sample 
  

   18-40 
  to 
  18*57 
  at 
  — 
  9°'7 
  C. 
  On 
  being 
  heated 
  or 
  cooled 
  the 
  

   substance 
  took 
  a 
  considerable 
  time 
  to 
  attain 
  a 
  constant 
  

   pressure 
  ; 
  this 
  very 
  slow 
  process 
  was 
  hastened 
  by 
  introducing 
  

   a 
  stirrer 
  which 
  was 
  moved 
  by 
  a 
  large 
  electromagnet 
  surround- 
  

   ing 
  the 
  Dewar 
  vessel. 
  We 
  extended 
  our 
  observations 
  above 
  

   0° 
  C. 
  up 
  to 
  the 
  critical 
  point 
  for 
  the 
  sake 
  of 
  comparison 
  with 
  

   former 
  results 
  for 
  ethane*. 
  The 
  agreement 
  was 
  satisfactory, 
  

   especially 
  if 
  the 
  small 
  error 
  of 
  our 
  earlier 
  air-gauge 
  be 
  taken 
  

   into 
  account. 
  Nevertheless 
  we 
  cannot 
  consider 
  the 
  vapour- 
  

   pressures 
  as 
  accurate 
  within 
  one 
  per 
  cent. 
  

  

  It 
  had 
  struck 
  us 
  that 
  ethane, 
  whose 
  pressures 
  at 
  ordinary 
  

   temperatures 
  are 
  much 
  lower 
  than 
  those 
  of 
  carbon 
  dioxide, 
  has 
  

   higher 
  pressures 
  at 
  very 
  low 
  temperatures. 
  It 
  appears, 
  how- 
  

   ever, 
  from 
  our 
  results 
  that 
  this 
  is 
  entirely 
  due 
  to 
  the 
  solidifica- 
  

   tion 
  of 
  carbon 
  dioxide, 
  the 
  liquid 
  curve 
  for 
  this 
  substance, 
  as 
  

   far 
  as 
  we 
  could 
  follow 
  it, 
  remaining 
  above 
  the 
  ethane 
  curve. 
  

   The 
  two 
  liquid 
  curves 
  do 
  not 
  intersect, 
  and 
  so 
  far 
  there 
  is 
  no 
  

   •evidence 
  of 
  association 
  of 
  liquid 
  carbon 
  dioxide. 
  The 
  

   ethane 
  curve 
  intersects 
  the 
  solid 
  carbon-dioxide 
  curve 
  at 
  

   -63° 
  C. 
  

   University 
  College, 
  Dundee. 
  

  

  XVI. 
  A 
  Voltameter 
  for 
  Small 
  Currents. 
  

   By^i.A. 
  Lehfeldtj-. 
  

  

  IN 
  the 
  course 
  of 
  some 
  experiments 
  with 
  mercury 
  volta- 
  

   meters 
  I 
  had 
  a 
  conversation 
  with 
  Mr. 
  E. 
  0. 
  (J. 
  Baly, 
  

   during 
  which 
  the 
  suggestion 
  of 
  a 
  remarkably 
  simple 
  form 
  

   of 
  instrument 
  arose. 
  This 
  I 
  have 
  realized 
  in 
  practice, 
  as 
  

   follows 
  : 
  — 
  

  

  A 
  glass 
  tube 
  of 
  from 
  0*5 
  to 
  1*5 
  mm. 
  bore 
  is 
  provided 
  with 
  

   n 
  pair 
  of 
  platinum 
  electrodes, 
  sealed 
  in 
  near 
  the 
  ends 
  ; 
  the 
  

   ends 
  are 
  then 
  drawn 
  out 
  to 
  a 
  small 
  diameter. 
  The 
  tube 
  so 
  

   prepared 
  is 
  filled 
  — 
  by 
  means 
  of 
  the 
  water-pump 
  — 
  with 
  

   mercury 
  throughout, 
  except 
  for 
  one 
  drop 
  of 
  mercurous-nitrate 
  

   solution 
  in 
  the 
  middle 
  of 
  its 
  length 
  ; 
  the 
  ends 
  of 
  the 
  tube 
  

   are 
  then 
  sealed 
  off. 
  The 
  tube 
  is 
  placed 
  vertically, 
  and 
  the 
  

   upper 
  portion 
  of 
  mercury 
  made 
  the 
  anode, 
  the 
  lower 
  the 
  

   cathode. 
  The 
  drop 
  of 
  solution 
  creeps 
  up 
  the 
  tube 
  at 
  a 
  rate 
  

   proportional 
  to 
  the 
  current 
  flowing, 
  the 
  movement 
  being 
  

  

  * 
  Phil. 
  Mag. 
  [5] 
  xliv. 
  p. 
  174. 
  

  

  t 
  Communicatee! 
  by 
  the 
  Physical 
  Society: 
  read 
  Nov. 
  8, 
  1901. 
  

  

  