﻿OF 
  SINGLE-ACTING 
  EXPANSIVE 
  STEAM-ENGINES. 
  203 
  

  

  Fuel 
  for 
  6000 
  lb. 
  of 
  steam 
  at 
  0-01d., 
  . 
  . 
  . 
  £0-2500 
  

   Interest 
  on 
  £0-432, 
  at 
  5 
  per 
  cent. 
  0-0216 
  

  

  h 
  = 
  £0-2716 
  

  

  Estimating 
  the 
  cost 
  of 
  the 
  engine 
  at 
  £250 
  per 
  square 
  foot 
  of 
  piston, 
  we 
  find 
  

   k= 
  5 
  per 
  cent, 
  per 
  annum 
  on 
  £250 
  = 
  £125, 
  

  

  and 
  ^ 
  = 
  0-0217; 
  ^r 
  = 
  5-144 
  

  

  F 
  1 
  

   The 
  line 
  BOA, 
  then, 
  is 
  to 
  be 
  drawn 
  so 
  that 
  its 
  ordinates 
  are 
  p-*= 
  j^s. 
  

  

  The 
  point 
  C 
  is 
  taken 
  on 
  this 
  line, 
  at 
  -rry 
  = 
  5-144 
  divisions 
  of 
  the 
  axis 
  of 
  

  

  abscissae 
  to 
  the 
  left 
  of 
  O 
  Y. 
  

  

  The 
  tangent 
  C 
  T 
  being 
  drawn, 
  is 
  found 
  to 
  touch 
  the 
  locus 
  of 
  Z 
  at 
  2*800 
  divi- 
  

   sions 
  to 
  the 
  right 
  of 
  O 
  Y. 
  

  

  Then 
  s= 
  2*800 
  is 
  the 
  ratio 
  of 
  expansion 
  sought, 
  corresponding 
  to 
  the 
  greatest 
  

   economy. 
  

  

  If 
  we 
  make 
  c=0*05 
  as 
  in 
  Mr 
  Wicksteed's 
  engine, 
  then 
  the 
  fraction 
  of 
  the 
  stroke 
  

   to 
  be 
  performed 
  at 
  full 
  pressure 
  is 
  

  

  y 
  =0-323 
  

  

  being 
  nearly 
  the 
  same 
  as 
  in 
  experiment 
  F. 
  

  

  The 
  mean 
  resistance 
  of 
  the 
  useful 
  load 
  per 
  square 
  foot 
  of 
  piston 
  is 
  

  

  R= 
  -P,-F 
  = 
  1713-6 
  lb. 
  

  

  s 
  l 
  

  

  The 
  duty 
  of 
  one 
  square 
  foot 
  of 
  piston 
  per 
  hour, 
  — 
  

  

  Rln 
  = 
  8,225,300 
  foot-lb. 
  

  

  And 
  one 
  horse-power 
  being 
  1,980,000 
  foot-lb. 
  per 
  hour, 
  the 
  real 
  horse-power 
  

   of 
  the 
  engine 
  is 
  

  

  4-154 
  per 
  square 
  foot 
  of 
  piston. 
  

  

  The 
  duty 
  of 
  one 
  pound 
  of 
  steam 
  is 
  

  

  RVj* 
  = 
  97,154 
  foot-lb. 
  

  

  To 
  give 
  an 
  example 
  of 
  a 
  special 
  case, 
  let 
  the 
  duty 
  to 
  be 
  performed 
  be 
  198,000,000 
  

   foot-pounds 
  per 
  hour, 
  being 
  equal 
  to 
  100 
  real 
  horse-power, 
  for 
  6000 
  hours 
  per 
  

   annum. 
  This 
  being 
  called 
  E, 
  we 
  find 
  from 
  the 
  above 
  data 
  that 
  the 
  area 
  of 
  piston 
  

   required 
  is 
  

  

  A= 
  — 
  ^- 
  =24-072 
  square 
  feet. 
  

   B, 
  In 
  ^ 
  

  

  The 
  consumption 
  of 
  steam 
  per 
  hour 
  is 
  

  

  W== 
  fr 
  ^-=20381b. 
  

   R 
  Vj 
  s 
  

  

  which 
  requires 
  2038 
  x 
  0*016=32-608 
  tons 
  of 
  boilers. 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  3 
  H 
  

  

  