﻿484 
  

  

  Mr. 
  W. 
  C. 
  Roberts 
  on 
  

  

  mined, 
  and 
  the 
  adoption 
  of 
  Eegnault's 
  numbers 
  in 
  calculating 
  the 
  heat 
  

   carried 
  into 
  the 
  calorimeter 
  by 
  the 
  alloys 
  may 
  tend 
  to 
  make 
  the 
  results 
  a 
  

   few 
  degrees 
  too 
  high. 
  

  

  The 
  results 
  of 
  the 
  experiments 
  were 
  calculated 
  by 
  means 
  of 
  the 
  fol- 
  

   lowing 
  formula 
  : 
  — 
  

  

  (P+p, 
  c,+p„c 
  u 
  ) 
  (e-Q 
  

  

  x 
  ~ 
  jp(T.-ej 
  

  

  where 
  p 
  is 
  the 
  weight 
  of 
  the 
  iron 
  employed. 
  

   P 
  „ 
  „ 
  water. 
  

  

  p 
  t 
  c 
  and 
  p 
  n 
  e 
  u 
  are 
  the 
  water-equivalents 
  of 
  the 
  calorimeter 
  and 
  ther- 
  

   mometer 
  respectively. 
  

   T 
  is 
  the 
  initial 
  temperature 
  of 
  the 
  iron. 
  

   t 
  ,, 
  water. 
  

   9 
  „ 
  final 
  „ 
  

   x 
  „ 
  specific 
  heat 
  required. 
  

  

  In 
  one 
  experiment 
  these 
  quantities 
  had 
  the 
  following 
  values 
  : 
  — 
  

  

  p 
  = 
  83-140 
  grms. 
  T=1040°C. 
  

   P 
  =260-520 
  „ 
  t 
  = 
  16° 
  C. 
  

  

  p, 
  15-687 
  „ 
  G 
  = 
  63° 
  C. 
  

  

  The 
  weight 
  of 
  silver 
  carried 
  over 
  was 
  3'266 
  grms., 
  the 
  heating 
  effect 
  

   of 
  which 
  is 
  equivalent 
  to 
  that 
  of 
  1*306 
  grm. 
  of 
  iron. 
  Therefore 
  the 
  

   corrected 
  value 
  of 
  p 
  is 
  83*140 
  + 
  1*306 
  = 
  84-446 
  grms. 
  

  

  Substituting 
  these 
  values 
  in 
  the 
  above 
  equation, 
  

  

  (260*52 
  + 
  15*687)(63-16) 
  

   x 
  - 
  84-446(1040—63) 
  

   =•15734. 
  

  

  Three 
  successive 
  experiments 
  gave 
  

  

  •15795, 
  

   •15550, 
  

   •15734, 
  

  

  1 
  the 
  mean 
  -15693 
  being 
  finally 
  adopted*. 
  

  

  It 
  may 
  be 
  pointed 
  out 
  that 
  the 
  specific 
  heat 
  of 
  iron 
  as 
  thus 
  determined 
  

   includes 
  and 
  neutralizes 
  several 
  errors 
  which 
  are 
  incidental 
  to 
  this 
  method 
  

   of 
  determining 
  high 
  temperatures. 
  The 
  principal 
  of 
  these 
  are 
  : 
  — 
  (1) 
  the 
  

   loss 
  of 
  heat, 
  which 
  is 
  rendered 
  latent 
  by 
  the 
  small 
  amount 
  of 
  water 
  which 
  

   is 
  evaporated 
  ; 
  (2) 
  the 
  slight 
  difference 
  between 
  the 
  specific 
  heat 
  of 
  the 
  

   iron 
  and 
  the 
  specific 
  heat 
  of 
  the 
  oxide 
  formed 
  on 
  its 
  surface 
  ; 
  (3) 
  the 
  loss 
  

  

  * 
  Weinhold 
  gives 
  0*1567 
  as 
  the 
  mean 
  specific 
  heat 
  of 
  wrought 
  iron 
  between 
  0° 
  and 
  

   900° 
  C. 
  (Pogg. 
  Ann. 
  vol. 
  cxlix. 
  p. 
  214). 
  

  

  