﻿304 
  Holhorn 
  <& 
  Day 
  — 
  Thermoelectricity 
  in 
  Certain 
  Metals, 
  

  

  been 
  done 
  in 
  this 
  case 
  ; 
  in 
  fact 
  one 
  of 
  the 
  metals 
  — 
  gold* 
  — 
  oSers 
  

   a 
  remarkable 
  example 
  of 
  the 
  effect 
  of 
  slight 
  impurities 
  upon 
  

   the 
  temperature 
  coefficient 
  of 
  the 
  resistance. 
  

  

  In 
  connection 
  with 
  the 
  pure 
  metals 
  several 
  alloys 
  were 
  also 
  

   investigated 
  but 
  offered 
  no 
  exception 
  to 
  the 
  application 
  of 
  the 
  

   law. 
  

  

  The 
  metals, 
  with 
  the 
  exception 
  of 
  iridium 
  and 
  rhodium, 
  were 
  

   in 
  the 
  form 
  of 
  drawn 
  wires 
  of 
  O-e"""^ 
  diameter 
  ; 
  these 
  two 
  were 
  

   rolled 
  out 
  into 
  narrow 
  rectangular 
  strips 
  slightly 
  larger 
  than 
  

   the 
  wires. 
  Wires 
  as 
  well 
  as 
  strips 
  were 
  brought 
  to 
  a 
  bright 
  

   glow 
  electrically 
  before 
  being 
  used 
  and 
  their 
  homogeneity 
  

   tested 
  by 
  connecting 
  their 
  ends 
  with 
  a 
  galvanometer 
  while 
  

   lying 
  in 
  the 
  electric 
  oven, 
  the 
  temperature 
  being 
  maintained 
  

   first 
  at 
  500°, 
  then 
  at 
  1000°. 
  Only 
  the 
  two 
  gold 
  wires 
  Au^ 
  and 
  AUi 
  

   showed 
  any 
  considerable 
  effect, 
  an 
  electromotive 
  force 
  amount- 
  

   ing 
  to 
  60 
  microvolts 
  being 
  here 
  obtained. 
  The 
  palladium 
  wires 
  

   behaved 
  somewhat 
  peculiarly, 
  showing 
  an 
  electromotive 
  force 
  of 
  

   about 
  150 
  microvolts 
  when 
  first 
  laid 
  in 
  the 
  oven 
  at 
  1000° 
  and 
  half 
  

   as 
  much 
  at 
  500° 
  ; 
  this 
  decreased 
  in 
  a 
  short 
  time 
  to 
  less 
  than 
  a 
  

   third 
  of 
  the 
  original 
  value. 
  There 
  is 
  an 
  evident 
  connection 
  

   between 
  this 
  and 
  a 
  phenomenon 
  conspicuous 
  when 
  the 
  wires 
  

   were 
  first 
  heated 
  as 
  above 
  mentioned 
  ; 
  they 
  did 
  not 
  glow 
  uni- 
  

   formly 
  at 
  once, 
  but 
  several 
  sharply 
  defined 
  dark 
  stretches 
  were 
  

   noticeable 
  which 
  slowly 
  diminished 
  in 
  length 
  and 
  disappeared 
  

   after 
  some 
  ten 
  minutes, 
  the 
  wire 
  then 
  glowing 
  quite 
  uniformly. 
  

  

  The 
  electric 
  oven 
  consisted 
  of 
  several 
  concentric 
  tubes 
  of 
  clay 
  

   separated 
  by 
  air 
  spaces, 
  the 
  innermost 
  tube 
  carrying 
  a 
  coil 
  of 
  

   nickel 
  wire 
  which 
  could 
  be 
  freely 
  heated 
  to 
  1300°. 
  

  

  The 
  elements 
  were 
  heated 
  in 
  a 
  porcelain 
  tube 
  which 
  extended 
  

   through 
  the 
  oven 
  without 
  being 
  in 
  contact 
  with 
  it 
  except 
  on 
  the 
  

   outside 
  where 
  the 
  cold 
  projecting 
  ends 
  were 
  supported. 
  The 
  

   hot 
  junction 
  lay 
  in 
  the 
  middle 
  of 
  the 
  oven, 
  and 
  the 
  wires, 
  care- 
  

   fully 
  insulated 
  from 
  each 
  other, 
  were 
  carried 
  out 
  at 
  the 
  ends 
  

   to 
  the 
  cold 
  junctions 
  (0°). 
  

  

  For 
  the 
  temperature 
  measurement 
  a 
  platinum 
  — 
  platin-rho- 
  

   dium 
  thermo-element 
  was 
  used 
  which 
  had 
  been 
  compared 
  with 
  

   the 
  gas 
  thermometer 
  between 
  0° 
  and 
  1000°. 
  Assuming 
  that 
  one 
  

   junction 
  is 
  maintained 
  at 
  0° 
  while 
  the 
  other 
  is 
  heated 
  to 
  ^°, 
  it 
  is 
  

   possible 
  to 
  express 
  the 
  electromotive 
  force 
  of 
  the 
  element 
  

   between 
  300° 
  and 
  1000° 
  as 
  a 
  quadratic 
  function 
  of 
  t 
  within 
  the 
  

   limits 
  of 
  the 
  errors 
  of 
  observation. 
  Above 
  1000° 
  the 
  tem- 
  

   peratures 
  were 
  obtained 
  by 
  extrapolation 
  of 
  this 
  function. 
  

  

  With 
  this 
  standard 
  element 
  the 
  other 
  elements 
  were 
  severally 
  

   compared, 
  the 
  four 
  wires 
  being 
  melted 
  together 
  at 
  the 
  hot 
  

  

  *This 
  gold 
  wire 
  (Auo 
  of 
  the 
  table) 
  had 
  already 
  shown 
  surprising 
  behavior 
  in 
  

   its 
  electrical 
  and 
  thermal 
  conductivity 
  — 
  Jaeger 
  and 
  Diesselhorst, 
  Sitz. 
  Ber. 
  Berl. 
  

   Akad., 
  1899, 
  p. 
  719. 
  

  

  