﻿200 
  

  

  MR 
  W. 
  J. 
  M. 
  RANKINE 
  ON 
  THE 
  POWER 
  AND 
  ECONOMY 
  

  

  Comparison 
  of 
  the 
  Theory 
  with 
  Mr 
  Wicksteed's 
  Experiments 
  on 
  the 
  Cornish 
  Pumping 
  

  

  Engine 
  at 
  Old 
  Ford. 
  

  

  Number 
  

   of 
  Expe- 
  

   riments. 
  

  

  Pressure 
  in 
  

   the 
  Boiler, 
  

  

  lb. 
  per 
  

   square 
  inch. 
  

  

  Steam 
  cut 
  

   off 
  at 
  y 
  of 
  

   the 
  stroke. 
  

  

  Ratio 
  of 
  

  

  Expansion 
  

  

  s. 
  

  

  Maximum 
  

   Pressure 
  in 
  

  

  the 
  Cylin- 
  

   der, 
  lb. 
  per 
  

   square 
  inch. 
  

  

  Lb. 
  of 
  Steam 
  expended 
  

   per 
  stroke, 
  

  

  Difference. 
  

  

  Duty 
  of 
  one 
  lb. 
  of 
  

   Steam, 
  

  

  Difference. 
  

  

  By 
  

  

  Theory. 
  

  

  By 
  Expe- 
  

   riment. 
  

  

  By 
  

   Theory. 
  

  

  By 
  Expe- 
  

   riment. 
  

  

  B. 
  

  

  30-45 
  

  

  0-603 
  

  

  1-605 
  

  

  14-27 
  

  

  7-781 
  

  

  7536 
  

  

  -0-245 
  

  

  foot 
  -lbs. 
  

  

  71530 
  

  

  foot-lbs. 
  

  

  73860 
  

  

  + 
  2330 
  

  

  C. 
  

  

  33-20 
  

  

  0-477 
  

  

  1-988 
  

  

  15-59 
  

  

  6-963 
  

  

  6-463 
  

  

  -0-500 
  

  

  79936 
  

  

  86123 
  

  

  + 
  6187 
  

  

  D. 
  

  

  39-2 
  

  

  0-397 
  

  

  2-342 
  

  

  16-9 
  

  

  6-236 
  

  

  6-200 
  

  

  -0-036 
  

  

  89275 
  

  

  89776 
  

  

  + 
  501 
  

  

  E. 
  

  

  41-2 
  

  

  0-352 
  

  

  2-605 
  

  

  17-89 
  

  

  5-905 
  

  

  5-985 
  

  

  + 
  0-085 
  

  

  94258 
  

  

  93002 
  

  

  -1256 
  

  

  F. 
  

  

  45-7 
  

  

  0-313 
  

  

  2-882 
  

  

  18-93 
  

  

  5-626 
  

  

  5-470 
  

  

  -0-156 
  

  

  98940 
  

  

  101756 
  

  

  + 
  2816 
  

  

  (1) 
  

  

  (2) 
  

  

  (3) 
  

  

  (4) 
  

  

  (5) 
  

  

  (6) 
  

  

  (7) 
  

  

  (3) 
  

  

  (9) 
  

  

  (10) 
  

  

  (11) 
  

  

  This 
  comparison 
  sufficiently 
  proves 
  that 
  the 
  results 
  of 
  the 
  theory 
  are 
  practically 
  

   correct. 
  

  

  It 
  is 
  remarkable, 
  that 
  in 
  every 
  instance 
  except 
  one 
  (experiment 
  E) 
  the 
  expe- 
  

   rimental 
  results 
  shew 
  a 
  somewhat 
  less 
  expenditure 
  of 
  steam 
  per 
  stroke, 
  and 
  a 
  

   greater 
  duty 
  per 
  pound 
  of 
  steam, 
  than 
  theory 
  indicates. 
  This 
  is 
  to 
  be 
  ascribed 
  to 
  

   the 
  fact, 
  that 
  although 
  the 
  action 
  of 
  the 
  steam 
  is 
  computed 
  theoretically, 
  on 
  the 
  

   assumption 
  that 
  during 
  the 
  expansion 
  it 
  is 
  cut 
  off 
  from 
  external 
  sources 
  of 
  heat, 
  

   yet 
  it 
  is 
  not 
  exactly 
  so 
  in 
  practice 
  ; 
  for 
  the 
  cylinder 
  is 
  surrounded 
  with 
  a 
  jacket 
  

   or 
  casing 
  communicating 
  with 
  the 
  boiler, 
  in 
  which 
  the 
  temperature 
  is 
  much 
  

   higher 
  than 
  the 
  highest 
  temperature 
  in 
  the 
  cylinder, 
  the 
  pressure 
  in 
  the 
  boiler 
  

   being 
  more 
  than 
  double 
  the 
  maximum 
  pressure 
  of 
  the 
  steam 
  when 
  working, 
  as 
  

   columns 
  (2) 
  and 
  (5) 
  shew. 
  There 
  is, 
  therefore, 
  a 
  portion 
  of 
  steam, 
  of 
  whose 
  

   amount 
  no 
  computation 
  can 
  be 
  made, 
  which 
  circulates 
  between 
  the 
  boiler 
  and 
  the 
  

   jacket, 
  serving 
  to 
  convey 
  heat 
  to 
  the 
  cylinder, 
  and 
  thus 
  augment 
  by 
  a 
  small 
  quan- 
  

   tity 
  the 
  action 
  of 
  the 
  steam 
  expended 
  ; 
  and 
  hence 
  the 
  formulas 
  almost 
  always 
  

   err 
  on 
  the 
  safe 
  side. 
  

  

  Supposing 
  one 
  pound 
  of 
  the 
  best 
  Welsh 
  coals 
  to 
  be 
  capable 
  (as 
  found 
  by 
  Mr 
  

   Wicksteed) 
  of 
  evaporating 
  9 
  493 
  lb. 
  of 
  water 
  at 
  the 
  pressure 
  in 
  the 
  boiler 
  during 
  

   the 
  experiment 
  F, 
  then 
  the 
  duty 
  of 
  a 
  Cornish 
  bushel, 
  or 
  94 
  lb. 
  of 
  such 
  coals, 
  in 
  

   the 
  circumstances 
  of 
  that 
  experiment 
  would 
  be 
  — 
  

  

  By 
  theory, 
  

   By 
  experiment, 
  

  

  88,288,000 
  ft. 
  lb. 
  

   90,801,000 
  - 
  

  

  Difference, 
  

  

  + 
  2,513,000 
  

  

  