﻿190 
  Mr. 
  E. 
  P. 
  Harrison 
  on 
  the 
  Temperature 
  Variation 
  of 
  

  

  After 
  these 
  experiments 
  the 
  copper 
  was 
  exceedingly 
  bright 
  

   while 
  the 
  iron 
  was 
  covered 
  with 
  a 
  black 
  deposit. 
  

  

  (iii.) 
  When 
  a 
  new 
  couple 
  is 
  heated 
  in 
  hydrogen, 
  Carve 
  H 
  I. 
  

   is 
  first 
  obtained, 
  no 
  change 
  of 
  slope 
  being 
  noticeable 
  and 
  the 
  

   values 
  for 
  the 
  E.M.F. 
  being 
  greater 
  than 
  those 
  obtained 
  in 
  a 
  

   vacuum. 
  This 
  curve 
  therefore 
  approximates 
  more 
  nearly 
  at 
  

   700° 
  to 
  the 
  one 
  obtained 
  at 
  lower 
  temperatures, 
  than 
  does 
  

   VI., 
  the 
  lowering 
  of 
  the 
  curve 
  under 
  the 
  influence 
  of 
  

   hydrogen 
  being 
  consistent 
  with 
  previous 
  observations 
  on 
  the 
  

   effect 
  of 
  this 
  gas. 
  

  

  (iv.) 
  After 
  continued 
  heating 
  in 
  hydrogen, 
  just 
  as 
  in 
  

   Curve 
  VjIL, 
  the 
  values 
  of 
  the 
  E.M.F. 
  become 
  less, 
  and 
  finally 
  

   the 
  curve 
  representing 
  them 
  lies 
  slightly 
  above 
  the 
  values 
  

   obtained 
  in 
  vacuo 
  (Curve 
  HIL). 
  HIL 
  is 
  nearly, 
  but 
  not 
  

   quite, 
  parallel 
  with 
  V 
  II. 
  The 
  wires 
  at 
  the 
  end 
  of 
  the 
  experi- 
  

   ments 
  were 
  both 
  perfectly 
  clean 
  although 
  the 
  iron 
  had 
  lost 
  

   its 
  polish. 
  The 
  copper 
  was 
  exceedingly 
  bright. 
  

  

  In 
  the 
  case 
  of 
  iron 
  heated 
  in 
  hydrogen, 
  possibly 
  a 
  gradual 
  

   reduction 
  of 
  impurities 
  in 
  the 
  substance 
  of 
  the 
  iron 
  accounts 
  

   for 
  the 
  change 
  in 
  the 
  E.M.F. 
  on 
  continued 
  heating. 
  

  

  [There 
  is 
  no 
  break 
  or 
  change 
  of 
  slope 
  in 
  the 
  thermoelectric 
  

   curves 
  for 
  Cu-Fe 
  at 
  800°, 
  the 
  temperature 
  at 
  which 
  the 
  

   resistance 
  of 
  Fe 
  alters.] 
  

  

  In 
  order 
  to 
  eliminate 
  any 
  possible 
  effect 
  of 
  the 
  copper, 
  a 
  

   Ni-Fe 
  couple 
  was 
  used. 
  The 
  E.M.F. 
  was 
  affected 
  by 
  

   continued 
  heating 
  in 
  hydrogen, 
  in 
  just 
  the 
  same 
  way 
  as 
  

   when 
  copper 
  was 
  present. 
  Evidently 
  the 
  effect 
  is 
  due 
  to 
  

   physical 
  or 
  chemical 
  changes 
  or 
  both 
  going 
  on 
  in 
  the 
  iron, 
  

   and 
  the 
  change 
  of 
  slope 
  at 
  895° 
  is 
  not 
  connected 
  with 
  a 
  

   decomposition 
  of 
  copper 
  oxide 
  at 
  this 
  temperature, 
  as 
  was 
  at 
  

   one 
  time 
  thought 
  possible. 
  

  

  Only 
  the 
  means 
  of 
  the 
  observations 
  of 
  E.M.F. 
  at 
  the 
  

   temperatures 
  of 
  steam, 
  aniline, 
  sulphur 
  vapour, 
  and 
  liquid 
  

   air 
  are 
  given 
  in 
  the 
  table 
  below. 
  

  

  The 
  observations 
  at 
  other 
  parts 
  of 
  the 
  curves 
  were 
  much 
  

   more 
  numerous 
  than 
  those 
  shown 
  by 
  circles 
  in 
  the 
  figures, 
  

   but 
  they 
  could 
  not 
  be 
  satisfactorily 
  represented 
  by 
  means 
  of 
  

   tables 
  or 
  empirical 
  formulas, 
  on 
  account 
  of 
  the 
  singularities 
  

   presented 
  in 
  the 
  variations 
  of 
  E.M.F. 
  The 
  E.M.F. 
  at 
  any 
  

   temperature 
  can 
  be 
  very 
  accurately 
  deduced 
  from 
  the 
  dif- 
  

   ference 
  curves, 
  e.g. 
  for 
  copper-iron 
  at 
  250° 
  

  

  the 
  parabolic 
  formula 
  gives 
  . 
  . 
  . 
  . 
  -f 
  1452*1 
  microvolts, 
  

   the 
  reading 
  of 
  Curve 
  D 
  (Fe) 
  gives 
  . 
  H- 
  1 
  7*5 
  „ 
  

  

  Hence 
  Total 
  E.M.F. 
  is 
  +1469*6 
  

  

  