﻿DYNAMICAL 
  THEORY 
  OF 
  HEAT. 
  275 
  

  

  (1.) 
  The 
  rate 
  of 
  variation 
  with 
  the 
  temperature, 
  of 
  the 
  pressure 
  of 
  saturated 
  

   steam. 
  

  

  (2.) 
  The 
  latent 
  heat 
  of 
  a 
  given 
  weight 
  of 
  saturated 
  steam. 
  

  

  (3.) 
  The 
  volume 
  of 
  a 
  given 
  weight 
  of 
  saturated 
  steam. 
  

  

  (4.) 
  The 
  volume 
  of 
  a 
  given 
  weight 
  of 
  water. 
  

  

  The 
  last 
  mentioned 
  of 
  these 
  elements 
  may, 
  on 
  account 
  of 
  the 
  manner 
  in 
  which 
  

   it 
  enters 
  the 
  formula, 
  be 
  taken 
  as 
  constant, 
  without 
  producing 
  any 
  appreciable 
  

   effect 
  on 
  the 
  probable 
  accuracy 
  of 
  the 
  result. 
  

  

  32. 
  Regnault's 
  observations 
  have 
  supplied 
  the 
  first 
  of 
  the 
  data 
  with 
  very 
  

   great 
  accuracy 
  for 
  all 
  temperatures 
  between 
  — 
  32° 
  cent, 
  and 
  230°. 
  

  

  33. 
  As 
  regards 
  the 
  second 
  of 
  the 
  data, 
  it 
  must 
  be 
  remarked 
  that 
  all 
  experi- 
  

   menters, 
  from 
  Watt, 
  who 
  first 
  made 
  experiments 
  on 
  the 
  subject, 
  to 
  Regnault, 
  

   whose 
  determinations 
  are 
  the 
  most 
  accurate 
  and 
  extensive 
  that 
  have 
  yet 
  been 
  

   made, 
  appear 
  to 
  have 
  either 
  explicitly 
  or 
  tacitly 
  assumed 
  the 
  same 
  principle 
  as 
  

   that 
  of 
  Carnot, 
  which 
  is 
  overturned 
  by 
  the 
  dynamical 
  theory 
  of 
  heat 
  ; 
  inas- 
  

   much 
  as 
  they 
  have 
  defined 
  the 
  " 
  total 
  heat 
  of 
  steam" 
  as 
  the 
  quantity 
  of 
  heat 
  

   required, 
  to 
  convert 
  a 
  unit 
  of 
  weight 
  of 
  water 
  at 
  0°, 
  into 
  steam 
  in 
  the 
  particular 
  

   state 
  considered. 
  Thus 
  Regnault, 
  setting 
  out 
  with 
  this 
  definition 
  for 
  " 
  the 
  

   total 
  heat 
  of 
  saturated 
  steam," 
  gives 
  experimental 
  determinations 
  of 
  it 
  for 
  the 
  

   entire 
  range 
  of 
  temperatures 
  from 
  0° 
  to 
  230° 
  ; 
  and 
  he 
  deduces 
  the 
  " 
  latent 
  heat 
  

   of 
  saturated 
  steam" 
  at 
  any 
  temperature, 
  from 
  the 
  " 
  total 
  heat," 
  so 
  determined, 
  

   by 
  subtracting 
  from 
  it 
  the 
  quantity 
  of 
  heat 
  necessary 
  to 
  raise 
  the 
  liquid 
  to 
  that 
  

   temperature. 
  Now, 
  according 
  to 
  the 
  dynamical 
  theory, 
  the 
  quantity 
  of 
  heat 
  

   expressed 
  by 
  the 
  preceding 
  definition 
  depends 
  on 
  the 
  manner 
  (which 
  may 
  be 
  

   infinitely 
  varied) 
  in 
  which 
  the 
  change 
  of 
  state 
  defined 
  is 
  effected 
  ; 
  differing 
  in 
  

   different 
  cases 
  by 
  the 
  thermal 
  equivalents 
  of 
  the 
  differences 
  of 
  the 
  external 
  mecha- 
  

   nical 
  effect 
  produced 
  in 
  the 
  expansion. 
  For 
  instance, 
  the 
  final 
  quantity 
  of 
  heat 
  

   required 
  to 
  evaporate 
  a 
  quantity 
  of 
  water 
  at 
  0°, 
  and 
  then, 
  keeping 
  it 
  always 
  in 
  

   the 
  state 
  of 
  saturated 
  vapour,* 
  bring 
  it 
  to 
  the 
  temperature 
  100°, 
  cannot 
  be 
  so 
  

   much 
  as 
  three-fourths 
  of 
  the 
  quantity 
  required, 
  first, 
  to 
  raise 
  the 
  temperature 
  of 
  

   the 
  liquid 
  to 
  100°, 
  and 
  then 
  evaporate 
  it 
  at 
  that 
  temperature 
  ; 
  and 
  yet 
  either 
  

   quantity 
  is 
  expressed 
  by 
  what 
  is 
  generally 
  received 
  as 
  a 
  definition 
  of 
  the 
  " 
  total 
  

   heat" 
  of 
  the 
  saturated 
  vapour. 
  To 
  find 
  what 
  it 
  is 
  that 
  is 
  really 
  determined 
  as 
  

   " 
  total 
  heat" 
  of 
  saturated 
  steam 
  in 
  Regnault's 
  researches, 
  it 
  is 
  only 
  necessary 
  to 
  

  

  * 
  See 
  below 
  (Part 
  III. 
  § 
  58), 
  where 
  the 
  " 
  negative 
  " 
  specific 
  heat 
  of 
  saturated 
  steam 
  is 
  

   investigated. 
  If 
  the 
  mean 
  value 
  of 
  this 
  quantity 
  between 
  0° 
  and 
  100° 
  were 
  — 
  1-5 
  (and 
  it 
  cannot 
  

   differ 
  much 
  from 
  this) 
  there 
  would 
  be 
  150 
  units 
  of 
  heat 
  emitted 
  by 
  a 
  pound 
  of 
  saturated 
  vapour 
  in 
  

   having 
  its 
  "temperature 
  raised 
  (by 
  compression) 
  from 
  0° 
  to 
  100°. 
  The 
  latent 
  heat 
  of 
  the 
  vapour 
  at 
  

   0° 
  being 
  606-5, 
  the 
  final 
  quantity 
  of 
  heat 
  required 
  to 
  convert 
  a 
  pound 
  of 
  water 
  at 
  0° 
  into 
  saturated 
  

   steam 
  at 
  100°, 
  in 
  the 
  first 
  of 
  the 
  ways 
  mentioned 
  in 
  the 
  text, 
  would 
  consequently 
  be 
  456-5, 
  which 
  is 
  

   only 
  about 
  f 
  of 
  the 
  quantity 
  637 
  found 
  as 
  " 
  the 
  total 
  heat'' 
  of 
  the 
  saturated 
  vapour 
  at 
  100°, 
  by 
  

   Regnault. 
  

  

  