﻿High 
  Temperatures. 
  187 
  

  

  The 
  volume 
  of 
  the 
  bnlb 
  at 
  0° 
  was 
  208*222'^'^°^ 
  and 
  the 
  

   weight 
  308 
  grams. 
  The 
  final 
  determination 
  of 
  the 
  volume 
  

   was 
  made 
  after 
  the 
  bulb 
  had 
  been 
  several 
  times 
  heated 
  to 
  the 
  

   highest 
  temperature 
  observed. 
  The 
  volume 
  was 
  chosen 
  larger 
  

   than 
  in 
  the 
  case 
  of 
  the 
  porcelain 
  bulbs 
  previously 
  used 
  in 
  order 
  

   to 
  still 
  further 
  diminish 
  the 
  effect 
  of 
  the 
  unheated 
  space. 
  

   The 
  required 
  connection 
  here 
  was 
  thus 
  only 
  1' 
  1 
  per 
  cent 
  oft 
  

   at 
  500" 
  and 
  1-9 
  per 
  cent 
  at 
  1100°, 
  

  

  Before 
  being 
  attached 
  to 
  the 
  thermometer 
  the 
  bulb 
  was 
  

   boiled 
  for 
  several 
  days 
  in 
  concentrated 
  nitric 
  acid. 
  When 
  

   heated 
  to 
  1100° 
  or 
  1200° 
  the 
  outside 
  surface 
  turned 
  black, 
  a 
  

   phenomenon 
  probably 
  to 
  be 
  attributed 
  to 
  the 
  oxidation 
  of 
  the 
  

   iridium. 
  Afterward, 
  when 
  the 
  temperature 
  was 
  carried 
  up 
  to 
  

   1300° 
  the 
  bright 
  metallic 
  color 
  returned 
  — 
  indicating 
  a 
  reduc- 
  

   tion 
  of 
  the 
  iridium 
  oxide. 
  

  

  Gas 
  filling. 
  — 
  Before 
  filling 
  the 
  bulb 
  with 
  gas 
  it 
  was 
  

   exhausted 
  with 
  the 
  mercury 
  pump 
  and 
  in 
  this 
  condition 
  heated, 
  

   at 
  first 
  to 
  850°, 
  afterward 
  to 
  1300°^ 
  the 
  pump 
  being 
  operated 
  

   from 
  time 
  to 
  time 
  throughout 
  and 
  a 
  sharp 
  vacuum 
  maintained 
  

   even 
  at 
  the 
  latter 
  temperature. 
  

  

  For 
  the 
  purpose 
  of 
  liaving 
  an 
  elementary 
  gas 
  for 
  the 
  final 
  

   measurements, 
  nitrogen 
  was 
  generated 
  from 
  ammonium 
  nitrite 
  

   and 
  passed 
  through 
  four 
  wash 
  bottles 
  containing 
  the 
  usual 
  

   pyrogallic 
  acid 
  solution, 
  then 
  through 
  drying 
  tubes 
  and 
  into 
  

   the 
  hot 
  bulb, 
  which 
  was 
  then 
  allowed 
  to 
  cool. 
  When 
  it 
  had 
  

   cooled 
  down 
  to 
  the 
  temperature 
  of 
  the 
  room 
  a 
  further 
  small 
  

   quantity 
  of 
  gas 
  was 
  added 
  or 
  taken 
  away 
  until 
  the 
  pressure 
  

   desired 
  for 
  the 
  observations 
  was 
  obtained. 
  This 
  pressure 
  was 
  

   always 
  so 
  chosen 
  that 
  at 
  the 
  highest 
  temperature 
  to 
  be 
  meas- 
  

   ured, 
  the 
  maximum 
  pressure 
  exerted 
  upon 
  the 
  walls 
  of 
  the 
  

   bulb 
  would 
  not 
  be 
  above 
  one 
  atmosphere. 
  

  

  Electric 
  Oven. 
  — 
  The 
  oven 
  was 
  similar 
  to 
  that 
  used 
  in 
  heating 
  

   the 
  porcelain 
  bulbs 
  ; 
  unfortunately, 
  however, 
  the 
  tubes 
  at 
  our 
  

   disposal 
  upon 
  which 
  the 
  coils 
  could 
  be 
  wound 
  were 
  a 
  few 
  milli- 
  

   meters 
  smaller 
  than 
  might 
  have 
  been 
  desired, 
  thereby 
  giving 
  

   rise 
  to 
  two 
  sorts 
  of 
  difficulties. 
  First, 
  the 
  irregularities 
  of 
  

   temperature 
  within 
  the 
  oven 
  made 
  themselves 
  strongly 
  felt 
  on 
  

   the 
  bulb 
  of 
  the 
  thermometer, 
  and 
  secondly, 
  inasmuch 
  as 
  the 
  

   space 
  between 
  bulb 
  and 
  oven 
  wall 
  was 
  very 
  narrow 
  the 
  wires 
  

   of 
  the 
  thermo-elements 
  were 
  with 
  difficulty 
  prevented 
  from 
  

   short 
  circuiting 
  through 
  the 
  metallic 
  wall 
  of 
  the 
  bulb. 
  Their 
  

   insulation 
  was 
  accomplished 
  in 
  these 
  experiments 
  hj 
  very 
  thin 
  

   porcelain 
  tubes 
  slipped 
  on 
  to 
  the 
  elements 
  wherever 
  such 
  a 
  

   contact 
  was 
  possible. 
  At 
  temperatures 
  of 
  1000° 
  and 
  above, 
  

   however, 
  where 
  the 
  porcelain 
  begins 
  to 
  act 
  sensibly 
  as 
  a 
  con- 
  

   ductor, 
  a 
  leakage 
  began 
  to 
  be 
  noticeable 
  from 
  the 
  oven 
  coil 
  into 
  

  

  