﻿MECHANICAL 
  ACTION 
  OF 
  HEAT. 
  175 
  

  

  The 
  coefficient 
  -305 
  K 
  w 
  =382 
  feet 
  per 
  centigrade 
  degree 
  is 
  the 
  apparent 
  specific 
  

   heat 
  of 
  steam 
  at 
  constant 
  pressure 
  ; 
  that 
  is 
  to 
  say, 
  for 
  steam, 
  — 
  

  

  k+ri 
  — 
  iv? 
  = 
  382 
  feet 
  P 
  er 
  centigrade 
  degree, 
  

  

  but 
  7s 
  — 
  ^=153 
  feet. 
  

  

  Therefore 
  the 
  real 
  specific 
  heat 
  of 
  steam 
  is 
  

  

  ft 
  = 
  7s-^rncr 
  = 
  229 
  feet 
  per 
  centigrade 
  degree, 
  

  

  = 
  127 
  - 
  4 
  feet 
  per 
  deg. 
  of 
  Fahrenheit. 
  

   = 
  K 
  w 
  x-183 
  

  

  A 
  TVT 
  153 
  2 
  

  

  and 
  N 
  = 
  229 
  = 
  g- 
  

  

  } 
  . 
  . 
  . 
  (36.) 
  

  

  The 
  quantity 
  - 
  / 
  x 
  dV 
  . 
  v 
  has 
  been 
  neglected, 
  as 
  already 
  explained, 
  in 
  these 
  

   ■J 
  F 
  

  

  calculations, 
  on 
  account 
  of 
  its 
  smallness. 
  When 
  t 
  = 
  C, 
  or 
  the 
  fixed 
  point 
  is 
  3 
  

  

  centigrade, 
  this 
  integral 
  is 
  nearly 
  equal 
  to 
  

  

  "^=-%O^M—^-X 
  T 
  ' 
  ■ 
  ' 
  ■ 
  < 
  37 
  -> 
  

  

  which, 
  for 
  steam, 
  is 
  equal 
  to 
  

  

  v 
  

  

  -K 
  w 
  x-122=f 
  Tl 
  

  

  V 
  

  

  For 
  a 
  pressure 
  of 
  eight 
  atmospheres, 
  

  

  ^-=^2 
  nearly, 
  r 
  1= 
  445°-5 
  (T 
  = 
  170°-9 
  cent.) 
  

   consequently, 
  - 
  v 
  P 
  x 
  = 
  - 
  K 
  w 
  x 
  0°-22 
  cent. 
  

  

  a 
  quantity 
  much 
  less 
  than 
  the 
  limit 
  of 
  errors 
  of 
  observation 
  in 
  experiments 
  on 
  

   latent 
  heat. 
  

  

  This 
  shews 
  that 
  in 
  practice 
  we 
  are 
  justified 
  in 
  overlooking 
  the 
  influence 
  of 
  

   the 
  volume 
  of 
  the 
  liquid 
  water 
  on 
  the 
  heat 
  of 
  evaporation. 
  

  

  Section 
  IV. 
  — 
  Of 
  the 
  Mechanical 
  Action 
  of 
  Steam, 
  treated 
  as 
  a 
  Perfect 
  Gas, 
  

   and 
  the 
  Power 
  of 
  the 
  Steam-Engine. 
  

  

  (21.) 
  In 
  the 
  present 
  limited 
  state 
  of 
  our 
  experimental 
  knowledge 
  of 
  the 
  den- 
  

   sity 
  of 
  steam 
  at 
  pressures 
  differing 
  much 
  from 
  that 
  of 
  the 
  atmosphere, 
  it 
  is 
  desir- 
  

   able 
  to 
  ascertain 
  whether 
  any 
  material 
  error 
  is 
  likely 
  to 
  arise 
  from 
  treating 
  it 
  as 
  

   a 
  perfect 
  gas. 
  For 
  this 
  purpose 
  the 
  ratio 
  of 
  the 
  volume 
  of 
  steam 
  at 
  100° 
  centi- 
  

   grade, 
  under 
  the 
  pressure 
  of 
  one 
  atmosphere, 
  to 
  that 
  of 
  the 
  water 
  which 
  produces 
  

   it 
  at 
  4°1 
  centigrade, 
  as 
  calculated 
  theoretically 
  on 
  the 
  supposition 
  of 
  steam 
  being 
  

   a 
  perfect 
  gas, 
  is 
  to 
  be 
  compared 
  with 
  the 
  actual 
  ratio. 
  

   vol. 
  xx. 
  part 
  i. 
  3 
  a 
  

  

  