﻿210 
  MR 
  W. 
  J. 
  M. 
  RANKINE 
  ON 
  EXPANSIVE 
  MACHINES. 
  

  

  accounted 
  for 
  by 
  the 
  fact, 
  that 
  the 
  steam 
  for 
  each 
  stroke, 
  which 
  is 
  produced 
  in 
  

   the 
  boiler 
  in 
  about 
  seven 
  or 
  eight 
  seconds, 
  escapes 
  suddenly 
  into 
  the 
  cylinder 
  in 
  

   a 
  fraction 
  of 
  a 
  second. 
  

  

  Thirdly, 
  The 
  expansive 
  working 
  of 
  the 
  steam, 
  instead 
  of 
  being 
  continued 
  

   down 
  to 
  30° 
  centigrade, 
  the 
  temperature 
  of 
  the 
  condenser, 
  stops 
  at 
  a 
  much 
  higher 
  

   temperature, 
  74°*66. 
  This 
  is 
  the 
  most 
  important 
  cause 
  of 
  loss 
  of 
  power. 
  

  

  If 
  we 
  now 
  take 
  for 
  t 
  1 
  and 
  t 
  the 
  absolute 
  temperatures 
  at 
  the 
  beginning 
  and 
  

   end 
  of 
  the 
  expansive 
  working, 
  and 
  calculate 
  the 
  maximum 
  duty 
  of 
  one 
  pound 
  

   of 
  steam 
  by 
  Carnot's 
  Law 
  between 
  those 
  temperatures, 
  we 
  find, 
  — 
  

  

  Tj 
  = 
  107°-26 
  + 
  274°-6 
  = 
  381°- 
  86 
  

   t 
  = 
  74°-66 
  + 
  274°-6 
  = 
  349°-26 
  

  

  J- 
  =0-08542 
  

  

  H 
  1 
  = 
  564°-5; 
  .-. 
  n= 
  48°22 
  

  

  To 
  this 
  has 
  to 
  he 
  added 
  the 
  duty, 
  at 
  full 
  pressure, 
  of 
  steam 
  at 
  t 
  , 
  dimi- 
  

   nished 
  by 
  one-third 
  for 
  back-pressure 
  and 
  friction, 
  and 
  by 
  one-fifteenth 
  

   for 
  liquefaction 
  in 
  the 
  cylinder, 
  = 
  ....... 
  23 
  9, 
  14 
  

  

  The 
  whole 
  amounting 
  to 
  71°36 
  

  

  Which 
  agrees 
  very 
  nearly 
  with 
  73°23, 
  the 
  observed 
  duty, 
  and 
  almost 
  exactly 
  

   with 
  71 
  °% 
  the 
  duty 
  as 
  calculated 
  by 
  the 
  formulae 
  and 
  tables 
  of 
  Section 
  Fourth. 
  

  

  These 
  examples 
  shew 
  clearly 
  the 
  nature 
  and 
  causes 
  of 
  the 
  waste 
  of 
  heat 
  in 
  

   the 
  steam-engine. 
  

  

  