﻿176 
  MR 
  W. 
  J. 
  M. 
  RANKINE 
  ON 
  THE 
  

  

  The 
  weight 
  of 
  one 
  volume 
  of 
  water 
  at 
  4 
  D 
  1 
  centigrade 
  being 
  taken 
  as 
  unity, 
  

   that 
  of 
  half 
  a 
  volume 
  of 
  oxygen 
  at 
  0° 
  centigrade, 
  under 
  the 
  pressure 
  of 
  one 
  atmo- 
  

   sphere, 
  according 
  to 
  the 
  experiments 
  of 
  M. 
  Regnault, 
  is 
  0000714900 
  

   That 
  of 
  one 
  volume 
  of 
  hydrogen, 
  .... 
  0000089578 
  

  

  The 
  sum 
  being 
  ...... 
  0-000804478 
  

  

  The 
  reciprocal 
  of 
  this 
  sum 
  being 
  multiplied 
  by 
  2 
  -=j^ 
  = 
  1-364166 
  the 
  ratio 
  of 
  

  

  dilatation 
  of 
  a 
  perfect 
  gas 
  from 
  0° 
  to 
  100 
  centigrade) 
  the 
  result 
  gives, 
  for 
  the 
  

   volume 
  of 
  steam 
  of 
  saturation 
  at 
  100° 
  centigrade 
  as 
  compared 
  with 
  that 
  of 
  water 
  at 
  

  

  4-1 
  169572 
  

  

  And 
  for 
  its 
  density, 
  . 
  000058972 
  

  

  The 
  agreement 
  of 
  those 
  results 
  with 
  the 
  known 
  volume 
  and 
  density 
  of 
  steam 
  

   is 
  sufficiently 
  close 
  to 
  shew, 
  that 
  at 
  pressures 
  less 
  than 
  one 
  atmosphere, 
  it 
  may 
  be 
  

   regarded 
  as 
  a 
  gas 
  sensibly 
  perfect 
  ; 
  from 
  which 
  it 
  may 
  be 
  concluded, 
  that 
  in 
  the 
  

   absence 
  of 
  more 
  precise 
  data, 
  the 
  errors 
  arising 
  from 
  treating 
  it 
  as 
  a 
  perfect 
  gas 
  

   at 
  such 
  higher 
  pressures 
  as 
  occur 
  in 
  practice, 
  will 
  not 
  be 
  of 
  much 
  importance. 
  

  

  Representing, 
  then, 
  by 
  v 
  the 
  volume 
  of 
  unity 
  of 
  weight 
  of 
  water 
  at 
  4 
  1 
  cen- 
  

   tigrade, 
  that 
  of 
  unity 
  of 
  weight 
  of 
  steam 
  at 
  any 
  pressure 
  and 
  temperature 
  will 
  be 
  

   given 
  by 
  the 
  formula 
  

  

  r 
  1696 
  vrs 
  r 
  

   v 
  =^y- 
  • 
  T 
  • 
  • 
  • 
  (38-) 
  

  

  7z 
  representing 
  the 
  number 
  of 
  units 
  of 
  weight 
  per 
  unit 
  of 
  area 
  in 
  the 
  pressure 
  of 
  

   one 
  atmosphere, 
  and 
  (t) 
  the 
  absolute 
  temperature 
  at 
  which 
  the 
  pressure 
  of 
  satura- 
  

   tion 
  is 
  one 
  atmosphere 
  ; 
  being 
  for 
  the 
  centigrade 
  scale 
  374 
  -6, 
  and 
  for 
  Fahren- 
  

   heit's 
  scale 
  674-28. 
  

  

  The 
  mechanical 
  action 
  of 
  unity 
  of 
  weight 
  of 
  steam 
  at 
  the 
  temperature 
  t 
  and 
  

   pressure 
  P, 
  during 
  its 
  entrance 
  into 
  a 
  cylinder, 
  before 
  it 
  is 
  permitted 
  to 
  expand, 
  

   is 
  represented 
  by 
  the 
  product 
  of 
  its 
  pressure 
  and 
  volume, 
  or 
  by 
  

  

  pv 
  = 
  1696^ 
  t 
  

  

  (t) 
  

  

  The 
  coefficient 
  — 
  j— 
  — 
  represents 
  a 
  certain 
  depth 
  of 
  fall 
  per 
  degree 
  of 
  abso- 
  

   lute 
  temperature, 
  and 
  is 
  the 
  same 
  with 
  the 
  coefficient 
  ^ 
  — 
  ^ 
  already 
  referred 
  to. 
  

   By 
  taking 
  the 
  following 
  values 
  of 
  the 
  factors 
  : 
  — 
  

  

  t! 
  = 
  0016 
  cubic 
  foot 
  per 
  pound 
  avoirdupois, 
  

   txy:=2117 
  pounds 
  avoirdupois 
  per 
  square 
  foot, 
  

  

  we 
  find 
  this 
  coefficient 
  to 
  be 
  

  

  153-35 
  feet 
  = 
  46 
  - 
  74 
  metres 
  per 
  centigrade 
  degree, 
  | 
  

   85-19 
  feet 
  per 
  degree 
  of 
  Fahrenheit 
  ; 
  J 
  

  

  