﻿518 
  Dr. 
  Andrews 
  on 
  the 
  Physical 
  Properties 
  of 
  [June 
  17, 
  

  

  These 
  results 
  fully 
  confirm 
  the 
  conclusions 
  which 
  I 
  formerly 
  deduced 
  

   from 
  the 
  behaviour 
  of 
  carbonic 
  acid 
  at 
  48°, 
  viz. 
  that 
  while 
  the 
  curve 
  

   representing 
  its 
  volume 
  under 
  different 
  pressures 
  approximates 
  more 
  

   uearly 
  to 
  that 
  of 
  a 
  perfect 
  gas 
  as 
  the 
  temperature 
  is 
  higher, 
  the 
  con- 
  

   traction 
  is 
  nevertheless 
  greater 
  than 
  it 
  would 
  be 
  if 
  the 
  law 
  of 
  Boyle 
  

   held 
  good, 
  at 
  least 
  for 
  any 
  temperature 
  at 
  which 
  experiments 
  have 
  yet 
  

   been 
  made. 
  Erora 
  the 
  foregoing 
  experiments 
  it 
  appears 
  that 
  at 
  63°'7 
  

   carbonic 
  acid 
  gas, 
  under 
  a 
  pressure 
  of 
  223 
  atmospheres, 
  is 
  reduced 
  to 
  

   of 
  its 
  volume 
  under 
  one 
  atmosphere, 
  or 
  to 
  less 
  than 
  one 
  half 
  the 
  

   volume 
  it 
  ought 
  to 
  occupy 
  if 
  it 
  were 
  a 
  perfect 
  gas 
  and 
  contracted 
  in 
  

   conformity 
  with 
  Boyle's 
  law. 
  Even 
  at 
  100° 
  the 
  contraction 
  under 
  the 
  

   same 
  pressure 
  amounts 
  to 
  -t^ 
  t 
  part 
  of 
  the 
  whole. 
  Erom 
  these 
  obser- 
  

   vations 
  we 
  may 
  infer 
  by 
  analogy 
  that 
  the 
  critical 
  points 
  of 
  the 
  greater 
  

   number 
  of 
  the 
  gases 
  not 
  hitherto 
  liquefied 
  are 
  probably 
  far 
  below 
  the 
  

   lowest 
  temperatures 
  hitherto 
  attained, 
  and 
  that 
  they 
  are 
  not 
  likely 
  to 
  be 
  

   seen, 
  either 
  as 
  liquids 
  or 
  solids, 
  till 
  much 
  lower 
  temperatures 
  even 
  than 
  

   those 
  produced 
  by 
  liquid 
  nitrous 
  oxide 
  are 
  reached. 
  

  

  Law 
  of 
  Gay-Lussac. 
  — 
  That 
  the 
  law 
  of 
  Gay-Lussac 
  in 
  the 
  case 
  of 
  the 
  

   so-called 
  permanent 
  gases, 
  or 
  in 
  general 
  terms 
  of 
  gases 
  greatly 
  above 
  

   their 
  critical 
  points, 
  holds 
  good 
  at 
  least 
  at 
  ordinary 
  pressures, 
  within 
  

   the 
  limits 
  of 
  experimental 
  error, 
  is 
  highly 
  probable 
  from 
  the 
  experiments 
  

   of 
  Eegnault; 
  but 
  the 
  results 
  I 
  have 
  obtained 
  with 
  carbonic 
  acid 
  will 
  

   show 
  that 
  this 
  law, 
  like 
  that 
  of 
  Boyle, 
  is 
  true 
  only 
  in 
  certain 
  limiting 
  

   conditions 
  of 
  gaseous 
  matter, 
  and 
  that 
  it 
  wholly 
  fails 
  in 
  others. 
  It 
  will 
  be 
  

   shown 
  that 
  not 
  only 
  does 
  the 
  coefficient 
  of 
  expansion 
  change 
  rapidly 
  with 
  

   the 
  pressure, 
  but 
  that, 
  the 
  pressure 
  or 
  volume 
  remaining 
  constant, 
  the 
  coeffi- 
  

   cient 
  changes 
  with 
  the 
  temperature. 
  The 
  latter 
  result 
  was 
  first 
  obtained 
  

   from 
  a 
  set 
  of 
  preliminary 
  experiments, 
  in 
  which 
  the 
  expansion 
  of 
  carbonic 
  

   acid 
  under 
  a 
  pressure 
  of 
  17 
  atmospheres 
  was 
  observed 
  at 
  4°, 
  20°, 
  and 
  54°; 
  

   and 
  it 
  has 
  since 
  been 
  fully 
  confirmed 
  by 
  a 
  large 
  number 
  of 
  experiments 
  

   made 
  at 
  different 
  pressures 
  and 
  well-defined 
  temperatures. 
  These 
  expe- 
  

   riments 
  were 
  conducted 
  by 
  the 
  two 
  methods 
  commonly 
  known 
  as 
  the 
  

   method 
  of 
  constant 
  pressure 
  and 
  the 
  method 
  of 
  constant 
  volume. 
  The 
  

   two 
  methods, 
  except 
  in 
  the 
  limiting 
  conditions, 
  do 
  not 
  give 
  the 
  same 
  

   values 
  for 
  the 
  coefficient 
  of 
  expansion 
  ; 
  but 
  they 
  agree 
  in 
  this 
  respect, 
  that 
  

   at 
  high 
  pressures 
  the 
  value 
  of 
  that 
  coefficient 
  changes 
  with 
  the 
  tempera- 
  

   ture. 
  "While 
  I 
  have 
  confined 
  this 
  statement 
  to 
  the 
  actual 
  results 
  of 
  

   experiment, 
  I 
  have 
  no 
  doubt 
  that 
  future 
  observations 
  will 
  discover, 
  in 
  the 
  

   case, 
  at 
  least, 
  of 
  such 
  gases 
  as 
  carbonic 
  acid, 
  a 
  similar 
  but 
  smaller 
  change 
  

   in 
  the 
  value 
  of 
  the 
  coefficient 
  for 
  heat 
  at 
  low 
  pressures. 
  The 
  numerous 
  

   experiments 
  I 
  have 
  made 
  on 
  this 
  subject 
  will 
  shortly 
  be 
  communicated 
  

   in 
  detail 
  to 
  the 
  Society 
  ; 
  and 
  for 
  the 
  present 
  I 
  will 
  only 
  give 
  the 
  following 
  

   results 
  : 
  — 
  

  

  