﻿Vapour-Pressure* 
  of 
  Carbon 
  Dioxide. 
  151 
  

  

  The 
  differences 
  are 
  equally 
  distributed 
  between 
  positive 
  and 
  

   negative, 
  and 
  are 
  accounted 
  for 
  by 
  the 
  fact 
  that 
  the 
  readings 
  

   of 
  the 
  low-pressure 
  gauge 
  are 
  somewhat 
  inaccurate 
  at 
  the 
  

   small 
  volumes. 
  

  

  In 
  order 
  to 
  deduce 
  the 
  pressure 
  from 
  a 
  reading 
  on 
  a 
  closed 
  

   gas-gauge, 
  the 
  corrections 
  for 
  the 
  deviation 
  from 
  Boyle's 
  law 
  

   are 
  required. 
  For 
  the 
  calculation 
  of 
  these 
  corrections 
  are 
  

   available: 
  (1) 
  RegnaultY 
  measurements 
  from 
  1 
  up 
  to 
  25 
  

   atmospheres, 
  and 
  the 
  approximate 
  formula 
  deduced 
  by 
  him 
  

   from 
  his 
  observations 
  ; 
  and 
  (2) 
  A 
  magat's 
  measurements 
  from 
  

   25 
  atmospheres 
  upwards. 
  The 
  corrections 
  deduced 
  from 
  the 
  

   former 
  are 
  much 
  larger 
  than 
  those 
  deduced 
  from 
  the 
  latter. 
  

   This 
  difference 
  must 
  be 
  due 
  to 
  the 
  temperature 
  (8° 
  C.) 
  in 
  

   Regnault's 
  experiments 
  having 
  been 
  lower 
  than 
  in 
  Amagat's 
  

   (20° 
  C). 
  

  

  We 
  tried 
  to 
  obtain 
  a 
  set 
  of 
  consistent 
  corrections 
  from 
  

   ] 
  atmosphere 
  upwards, 
  by 
  reducing 
  as 
  well 
  as 
  we 
  could 
  

   Regnault's 
  corrections 
  to 
  the 
  temperature 
  of 
  Amagat's 
  

   observations 
  and 
  vice 
  versa. 
  The 
  corrections 
  thus 
  obtained 
  

   are 
  probably 
  fairly 
  accurate 
  up 
  to 
  25 
  atmospheres. 
  Above 
  

   this 
  pressure, 
  at 
  temperatures 
  differing 
  from 
  20° 
  C. 
  the 
  

   uncertainties 
  become 
  greater. 
  It 
  would 
  be 
  an 
  extremely 
  

   useful 
  work 
  to 
  repeat 
  Amagat's 
  experiments 
  at 
  a 
  lower 
  gauge- 
  

   temperature, 
  and 
  to 
  extend 
  them 
  to 
  pressures 
  from 
  1 
  to 
  25 
  

   atmospheres. 
  This 
  latter 
  part 
  is 
  within 
  the 
  scope 
  of 
  labora- 
  

   tory-research 
  work. 
  

  

  In 
  the 
  experiments 
  on 
  carbon 
  dioxide 
  the 
  gauges 
  were 
  used 
  

   as 
  above; 
  after 
  their 
  completion 
  the 
  low-pressure 
  gauge 
  was 
  

   filled 
  with 
  nitrogen, 
  so 
  that 
  in 
  the 
  later 
  experiments 
  both 
  

   gas-gauges 
  contained 
  nitrogen. 
  But 
  the 
  uncertainty 
  of 
  the 
  

   corrections 
  remains. 
  The 
  gauges 
  show 
  complete 
  agreement, 
  

   the 
  reading 
  at 
  the 
  same 
  pressure 
  being 
  26' 
  10 
  on 
  both. 
  

  

  4. 
  The 
  TJiermometer. 
  — 
  The 
  many 
  advantages 
  claimed 
  for 
  

   the 
  platinum 
  thermometer 
  induced 
  us 
  to 
  use 
  it 
  in 
  preference 
  

   to 
  a 
  gas-thermometer 
  or 
  thermoelectric 
  couple, 
  and 
  although 
  

   we 
  encountered 
  many 
  unexpected 
  difficulties, 
  we 
  found 
  it 
  

   quite 
  suitable 
  for 
  our 
  purpose. 
  It 
  may 
  be 
  of 
  interest 
  to 
  give 
  

   here 
  in 
  some 
  detail 
  an 
  account 
  of 
  our 
  experiences 
  with 
  this 
  

   instrument. 
  In 
  the 
  first 
  place, 
  we 
  are 
  inclined 
  to 
  doubt 
  the 
  

   statement 
  that 
  when 
  measurements 
  are 
  made 
  with 
  an 
  ordinary 
  

   post-office 
  bridge 
  results 
  may 
  be 
  obtained 
  which 
  are 
  consistent 
  

   to 
  a 
  few 
  hundredths 
  of 
  a 
  degree 
  up 
  to 
  500° 
  C* 
  Using 
  

   resistance-coils 
  and 
  wire-bridge 
  in 
  the 
  way 
  described 
  by 
  

   Callendarf, 
  and 
  allowing 
  for 
  coil 
  errors, 
  wire 
  calibration, 
  

  

  * 
  Preston, 
  'Heat,' 
  1894, 
  p. 
  148. 
  

   f 
  Phil, 
  Mag. 
  [5] 
  xxxii. 
  p. 
  107. 
  

  

  