﻿186 
  MR 
  W. 
  J. 
  M. 
  RANKINE 
  ON 
  THE 
  

  

  Whence, 
  the 
  heat 
  converted 
  in 
  power, 
  as 
  calculated 
  directly, 
  is, 
  

  

  95°-8 
  K 
  w 
  

  

  agreeing 
  with 
  the 
  calculation 
  from 
  the 
  power 
  produced. 
  

  

  95*8 
  

   In 
  this 
  example, 
  the 
  heat 
  rendered 
  effective 
  is 
  *= 
  <w» 
  or 
  somewhat 
  more 
  than 
  

  

  one-sixth 
  of 
  that 
  expended 
  in 
  the 
  boiler. 
  

  

  (33.) 
  The 
  results 
  of 
  the 
  calculations 
  of 
  maximum 
  possible 
  effect, 
  of 
  which 
  

   examples 
  have 
  just 
  been 
  given, 
  are 
  limits 
  which 
  may 
  be 
  approached 
  in 
  practice 
  

   by 
  Cornish 
  and 
  similar 
  engines, 
  but 
  which 
  cannot 
  be 
  fully 
  realised 
  ; 
  and 
  yet 
  it 
  

   has 
  been 
  shewn, 
  that 
  in 
  those 
  theoretical 
  cases 
  only 
  about 
  one-sixth 
  of 
  the 
  heat 
  

   expended 
  in 
  the 
  boiler 
  is 
  rendered 
  effective. 
  In 
  practice, 
  of 
  course, 
  the 
  propor- 
  

   tion 
  of 
  heat 
  rendered 
  effective 
  must 
  be 
  still 
  smaller 
  ; 
  and, 
  in 
  fact, 
  in 
  some 
  unex- 
  

   pansive 
  engines, 
  it 
  amounts 
  to 
  only 
  one-twenty-fourth, 
  or 
  even 
  less. 
  

  

  Dr 
  Lyon 
  Playfair, 
  in 
  a 
  memoir 
  on 
  the 
  Evaporating 
  Power 
  of 
  Fuel, 
  has 
  

   taken 
  notice 
  of 
  the 
  great 
  disproportion 
  between 
  the 
  heat 
  expended 
  in 
  the 
  steam- 
  

   engine 
  and 
  the 
  work 
  performed. 
  It 
  has 
  now 
  been 
  shewn 
  that 
  this 
  waste 
  of 
  heat 
  

   is, 
  to 
  a 
  great 
  extent, 
  a 
  necessary 
  consequence 
  of 
  the 
  nature 
  of 
  the 
  machine. 
  It 
  

   can 
  only 
  be 
  reduced 
  by 
  increasing 
  the 
  initial 
  pressure 
  of 
  the 
  steam, 
  and 
  the 
  extent 
  

   of 
  the 
  expansive 
  action 
  ; 
  and 
  to 
  both 
  of 
  those 
  resources 
  there 
  are 
  practical 
  limits, 
  

   which 
  have 
  already 
  in 
  some 
  instances 
  been 
  nearly 
  attained. 
  

  

  APPENDIX 
  TO 
  THE 
  FOURTH 
  SECTION, 
  

  

  CONTAINING 
  TABLES 
  TO 
  BE 
  USED 
  IN 
  CALCULATING 
  THE 
  PRESSURE, 
  VOLUME, 
  AND 
  MECHANICAL 
  

   ACTION 
  OF 
  STEAM, 
  TREATED 
  AS 
  A 
  PERFECT 
  GAS. 
  

  

  The 
  object 
  of 
  the 
  first 
  of 
  the 
  annexed 
  tables 
  is 
  to 
  facilitate 
  the 
  calculation 
  of 
  

   the 
  volume 
  of 
  steam 
  of 
  saturation 
  at 
  a 
  given 
  pressure, 
  of 
  the 
  pressure 
  of 
  steam 
  of 
  

   saturation 
  at 
  a 
  given 
  volume, 
  and 
  of 
  its 
  mechanical 
  action 
  at 
  full 
  pressure. 
  

  

  The 
  pressures 
  are 
  expressed 
  in 
  pounds 
  avoirdupois 
  per 
  square 
  foot, 
  and 
  the 
  

   volumes 
  by 
  the 
  number 
  of 
  cubic 
  feet 
  occupied 
  by 
  one 
  pound 
  avoirdupois 
  of 
  steam, 
  

   when 
  considered 
  as 
  a 
  perfect 
  gas 
  ; 
  those 
  denominations 
  being 
  the 
  most 
  convenieDt 
  

   for 
  mechanical 
  calculations 
  in 
  this 
  country. 
  

  

  The 
  columns 
  to 
  be 
  used 
  in 
  determining 
  the 
  pressure 
  from 
  the 
  volume, 
  and 
  

   vice 
  versa, 
  are 
  the 
  third, 
  fourth, 
  sixth, 
  and 
  seventh. 
  

  

  The 
  third 
  column 
  contains 
  the 
  common 
  logarithms 
  of 
  the 
  pressures 
  of 
  steam 
  

   of 
  saturation 
  for 
  every 
  fifth 
  degree 
  of 
  the 
  centigrade 
  thermometer 
  from 
  —30° 
  to 
  

   -i- 
  260° 
  : 
  that 
  is 
  to 
  say, 
  for 
  every 
  ninth 
  degree 
  of 
  Fahrenheit's 
  thermometer 
  from 
  

   -22° 
  to 
  +500°. 
  

  

  The 
  fourth 
  column 
  gives 
  the 
  differences 
  of 
  the 
  successive 
  terms 
  of 
  the 
  third 
  

   column. 
  

  

  