﻿1875.] 
  

  

  Matter 
  in 
  the 
  Liquid 
  and 
  Gaseous 
  States. 
  

  

  515 
  

  

  under 
  melted 
  lard. 
  In 
  this 
  way 
  the 
  air 
  enclosed 
  within 
  the 
  pores 
  of 
  the 
  

   leather 
  is 
  removed 
  without 
  the 
  use 
  of 
  water, 
  and 
  a 
  packing 
  is 
  obtained 
  

   so 
  perfect 
  that 
  it 
  appears, 
  as 
  far 
  as 
  my 
  experience 
  goes, 
  never 
  to 
  fail, 
  

   provided 
  it 
  is 
  used 
  in 
  a 
  vessel 
  filled 
  with 
  water. 
  It 
  is 
  remarkable, 
  how- 
  

   ever, 
  that 
  the 
  same 
  packing, 
  when 
  an 
  apparatus 
  specially 
  constructed 
  for 
  

   the 
  purpose 
  of 
  forged 
  iron 
  was 
  filled 
  with 
  mercury, 
  always 
  yielded, 
  even 
  

   at 
  a 
  pressure 
  of 
  40 
  atmospheres, 
  in 
  the 
  course 
  of 
  a 
  few 
  days. 
  

  

  It 
  is 
  with 
  regret 
  that 
  I 
  am 
  still 
  obliged 
  to 
  give 
  the 
  pressures 
  in 
  atmo- 
  

   spheres 
  as 
  indicated 
  by 
  an 
  air- 
  or 
  hydrogen-manometer, 
  without 
  attempt- 
  

   ing 
  for 
  the 
  present 
  to 
  apply 
  the 
  corrections 
  required 
  to 
  reduce 
  them 
  to 
  

   true 
  pressures. 
  The 
  only 
  satisfactory 
  method 
  of 
  obtaining 
  these 
  correc- 
  

   tions 
  would 
  be 
  to 
  compare 
  the 
  indications 
  of 
  the 
  manometer 
  with 
  those 
  

   of 
  a 
  column 
  of 
  mercury 
  of 
  the 
  requisite 
  length 
  ; 
  and 
  this 
  method, 
  as 
  is 
  

   known, 
  was 
  employed 
  by 
  Arago 
  and 
  Dulong, 
  and 
  afterwards 
  in 
  his 
  

   classical 
  researches 
  by 
  Eegnaulfc, 
  for 
  pressures 
  reaching 
  nearly 
  to 
  30 
  

   atmospheres. 
  For 
  this 
  moderate 
  pressure 
  a 
  column 
  of 
  mercury 
  about 
  

   23 
  metres, 
  or 
  75 
  feet, 
  in 
  length 
  had 
  to 
  be 
  employed. 
  For 
  pressures 
  

   corresponding 
  to 
  500 
  atmospheres, 
  at 
  which 
  I 
  have 
  no 
  difficulty 
  in 
  work- 
  

   ing 
  with 
  my 
  apparatus, 
  a 
  mercurial 
  column 
  of 
  the 
  enormous 
  height 
  of 
  

   380 
  metres, 
  or 
  1250 
  feet, 
  would 
  be 
  required. 
  Although 
  the 
  mechanical 
  

   difficulties 
  in 
  the 
  construction 
  of 
  a 
  long 
  tube 
  for 
  this 
  purpose 
  are 
  perhaps 
  

   not 
  insuperable, 
  it 
  could 
  only 
  be 
  mounted 
  in 
  front 
  of 
  some 
  rare 
  moun- 
  

   tain 
  escarpment, 
  where 
  it 
  would 
  be 
  practically 
  impossible 
  to 
  conduct 
  a 
  

   long 
  series 
  of 
  delicate 
  experiments. 
  About 
  three 
  years 
  ago 
  I 
  had 
  the 
  

   honour 
  of 
  submitting 
  to 
  the 
  Council 
  of 
  the 
  Society 
  a 
  proposal 
  for 
  con- 
  

   structing 
  an 
  apparatus 
  which 
  would 
  have 
  enabled 
  any 
  pressure 
  to 
  be 
  

   measured 
  by 
  the 
  successive 
  additions 
  of 
  the 
  pressure 
  of 
  a 
  column 
  of 
  

   mercury 
  of 
  a 
  fixed 
  length 
  ; 
  and 
  working 
  drawings 
  of 
  the 
  apparatus 
  were 
  

   prepared 
  by 
  Mr. 
  J. 
  Cumine, 
  whose 
  services 
  I. 
  am 
  glad 
  to 
  have 
  again 
  this 
  

   opportunity 
  of 
  acknowledging. 
  An 
  unexpected 
  difficulty, 
  however, 
  arose 
  

   in 
  consequence 
  of 
  the 
  packing 
  of 
  the 
  screws 
  (as 
  I 
  have 
  already 
  stated) 
  

   not 
  holding 
  when 
  the 
  leather 
  was 
  in 
  contact 
  with 
  mercury 
  instead 
  of 
  

   water, 
  and 
  the 
  apparatus 
  was 
  not 
  constructed. 
  For 
  two 
  years 
  the 
  

   problem 
  appeared, 
  if 
  not 
  theoretically, 
  to 
  be 
  practically 
  impossible 
  of 
  

   solution 
  ; 
  but 
  I 
  am 
  glad 
  now 
  to 
  be 
  able 
  to 
  announce 
  to 
  the 
  Society 
  that 
  

   another 
  method, 
  simpler 
  in 
  principle 
  and 
  free 
  from 
  the 
  objections 
  to 
  

   which 
  I 
  have 
  referred, 
  has 
  lately 
  suggested 
  itself 
  to 
  me, 
  by 
  means 
  of 
  

   which 
  it 
  will, 
  I 
  fully 
  expect, 
  be 
  possible 
  to 
  determine 
  the 
  rate 
  of 
  com- 
  

   pressibility 
  of 
  hydrogen 
  or 
  other 
  gas 
  by 
  direct 
  reference 
  to 
  the 
  weight 
  of 
  a 
  

   liquid 
  column, 
  or 
  rather 
  of 
  a 
  number 
  of 
  liquid 
  columns, 
  up 
  to 
  pressures 
  

   of 
  500 
  or 
  even 
  1000 
  atmospheres. 
  For 
  the 
  present 
  it 
  must 
  be 
  under- 
  

   stood 
  that, 
  in 
  stating 
  the 
  following 
  results, 
  the 
  pressures 
  in 
  atmospheres 
  

   are 
  deduced 
  from 
  the 
  apparent 
  compressibility, 
  in 
  some 
  cases 
  of 
  air, 
  in 
  

   others 
  of 
  hydrogen 
  gas, 
  contained 
  in 
  capillary 
  glass 
  tubes. 
  

  

  In 
  this 
  notice 
  I 
  will 
  only 
  refer 
  to 
  the 
  results 
  of 
  experiments 
  upon 
  

   carbonic 
  acid 
  gas 
  when 
  alone 
  or 
  when 
  mixed 
  with 
  nitrogen. 
  It 
  is 
  with 
  

  

  