﻿MECHANICAL 
  ACTION 
  OF 
  HEAT. 
  183 
  

  

  Consequently 
  to 
  give 
  the 
  maximum 
  useful 
  effect, 
  

  

  P 
  2 
  = 
  P 
  3 
  +/ 
  = 
  648 
  lb. 
  per 
  square 
  foot. 
  

  

  Total 
  pressure 
  of 
  the 
  steam 
  when 
  first 
  admitted, 
  P 
  1 
  = 
  72001b. 
  

   Volume 
  of 
  1 
  lb. 
  of 
  steam 
  V 
  1 
  = 
  8-7825 
  cubic 
  feet. 
  

   Therefore 
  ~P 
  l 
  V 
  x 
  = 
  63234 
  lbs. 
  raised 
  one 
  foot. 
  

  

  p 
  1 
  = 
  fi 
  _ 
  and 
  consequently, 
  

  

  Expansion 
  to 
  produce 
  the 
  maximum 
  useful 
  effect 
  s= 
  ( 
  p 
  1 
  J 
  7 
  =7*877 
  

  

  Space 
  traversed 
  by 
  the 
  piston 
  during 
  the 
  action 
  of 
  one 
  pound 
  of 
  steam, 
  

  

  = 
  Vj 
  (1-c) 
  s 
  = 
  65-886 
  cubic 
  feet. 
  

   Gross 
  effect 
  of 
  one 
  pound 
  of 
  steam, 
  in 
  pounds 
  raised 
  one 
  foot 
  high, 
  

  

  = 
  P 
  1 
  V 
  1 
  (7-6s 
  - 
  !-^-) 
  -P 
  3 
  V 
  1 
  (l-c)« 
  . 
  . 
  =112004 
  

  

  Deduct 
  for 
  resistance 
  of 
  engine 
  when 
  unloaded 
  fV 
  1 
  (1 
  — 
  c) 
  s 
  . 
  = 
  4744 
  

  

  Effect 
  of 
  one 
  pound 
  of 
  steam 
  in 
  overcoming 
  resistance 
  depending! 
  -|079fi0 
  

   on 
  useful 
  load, 
  ........ 
  J 
  

  

  This 
  being 
  multiplied 
  by 
  62£, 
  gives 
  for 
  the 
  effect 
  of 
  one 
  cubic 
  foot 
  

  

  of 
  water 
  evaporated, 
  in 
  pounds 
  raised 
  one 
  foot, 
  .... 
  6,703,750 
  

  

  It 
  is 
  here 
  necessary 
  to 
  observe, 
  that 
  M. 
  de 
  Pambour 
  distinguishes 
  the 
  useful 
  

   resistance 
  into 
  two 
  parts, 
  the 
  resistance 
  of 
  the 
  useful 
  load 
  independently 
  of 
  the 
  

   engine, 
  and 
  the 
  increase 
  in 
  the 
  resistance 
  of 
  the 
  engine, 
  arising 
  from 
  the 
  former 
  

   resistance, 
  and 
  found 
  by 
  multiplying 
  it 
  by 
  a 
  constant 
  fraction 
  which 
  he 
  calls 
  8. 
  

   In 
  calculating 
  the 
  net 
  useful 
  effect, 
  he 
  takes 
  into 
  account 
  the 
  former 
  portion 
  of 
  the 
  

   resistance 
  only 
  ; 
  consequently, 
  

  

  Net 
  useful 
  effect 
  as 
  defined 
  by 
  M. 
  DE 
  Pambour 
  = 
  r 
  ° 
  — 
  — 
  =£ 
  — 
  * 
  *■ 
  ~ 
  c 
  > 
  s 
  . 
  (54.) 
  

  

  J 
  1 
  + 
  8 
  v 
  

  

  The 
  value 
  of 
  8, 
  for 
  double 
  acting 
  steam-engines 
  generally, 
  is 
  considered 
  by 
  

   M. 
  de 
  Pambour 
  to 
  be 
  i 
  ; 
  consequently, 
  to 
  reduce 
  the 
  effect 
  of 
  one 
  cubic 
  foot 
  of 
  

   water 
  as 
  calculated 
  above 
  to 
  that 
  which 
  corresponds 
  with 
  his 
  definition, 
  we 
  must 
  

   deduct 
  |, 
  which 
  leaves, 
  

  

  5,865,781 
  lb. 
  raised 
  one 
  foot. 
  

  

  M. 
  de 
  Pambour's 
  own 
  calculation 
  gives, 
  

  

  6,277,560 
  

   being 
  too 
  large 
  by 
  about 
  one-fifteenth. 
  

  

  (32.) 
  In 
  order 
  to 
  shew 
  the 
  limit 
  of 
  the 
  effect 
  which 
  may 
  be 
  expected 
  from 
  the 
  

   expenditure 
  of 
  a 
  given 
  quantity 
  of 
  heat 
  in 
  evaporating 
  water, 
  and 
  also 
  to 
  verify 
  

   the 
  approximate 
  method 
  employed 
  in 
  calculating 
  the 
  expansive 
  action 
  of 
  the 
  

   steam, 
  I 
  shall 
  now 
  investigate 
  the 
  maximum 
  gross 
  effect, 
  including 
  resistance 
  of 
  

   all 
  kinds, 
  producible 
  by 
  evaporating 
  unity 
  of 
  weight 
  of 
  water 
  at 
  a 
  higher 
  tem- 
  

   perature 
  and 
  liquefying 
  it 
  at 
  a 
  lower, 
  and 
  compare, 
  in 
  two 
  examples, 
  the 
  power 
  

   produced, 
  with 
  the 
  heat 
  which 
  disappears 
  during 
  the 
  action 
  of 
  the 
  steam, 
  as 
  

   calculated 
  directly. 
  

  

  vol. 
  xx. 
  part 
  1. 
  3 
  c 
  

  

  