﻿186 
  Ilolhorn 
  and 
  Day 
  — 
  Gas 
  Thermometer 
  at 
  

  

  probably 
  a 
  chemical 
  action 
  or 
  a 
  setting 
  free 
  of 
  absorbed 
  gas 
  is 
  

   responsible 
  for 
  it. 
  If 
  porcelain 
  at 
  high 
  temperatures 
  were 
  

   porous 
  the 
  change 
  with 
  each 
  further 
  heating 
  should 
  be 
  as 
  great 
  

   as 
  with 
  the 
  first. 
  A 
  change 
  in 
  the 
  volume 
  of 
  the 
  bulb 
  cannot 
  

   explain 
  the 
  phenomenon, 
  for 
  bulb 
  Xo. 
  Ill 
  was 
  weighed 
  after 
  

   the 
  observations 
  and 
  its 
  volume 
  determined. 
  The 
  result 
  

   showed 
  an 
  increase 
  in 
  volume 
  amounting 
  to 
  0-003, 
  a 
  result 
  

   which 
  would 
  have 
  an 
  opposite 
  effect 
  to 
  that 
  under 
  considera- 
  

   tion. 
  

  

  Concerning 
  the 
  experiments 
  of 
  Teudt" 
  tending 
  to 
  show 
  a 
  

   dissociation 
  of 
  atmospheric 
  nitrogen 
  at 
  temperatures 
  below 
  

   •500° 
  in 
  which 
  connection 
  he 
  has 
  quoted 
  experiments 
  of 
  Hol- 
  

   born 
  and 
  Wien, 
  it 
  may 
  be 
  said 
  that 
  we 
  used 
  the 
  elsewhere 
  

   mentioned 
  platinum 
  bulb 
  at 
  first 
  with 
  atmospheric 
  nitrogen 
  at 
  

   temperatures 
  considerably 
  above 
  500° 
  and 
  detected 
  no 
  change 
  

   in 
  the 
  gas 
  whatever. 
  We 
  hope 
  also 
  later 
  to 
  investigate 
  the 
  

   behavior 
  of 
  porcelain 
  bulbs 
  with 
  chemically 
  pure 
  nitrogen 
  as 
  

   well. 
  

  

  6. 
  Experiments 
  with 
  the 
  platin-iridium 
  bulb. 
  

  

  The 
  Bulb. 
  — 
  The 
  platin-iridium 
  bulb 
  used 
  was 
  similar 
  in 
  form 
  

   to 
  the 
  glass 
  bulb 
  first 
  described 
  and 
  was 
  made 
  by 
  the 
  firm 
  of 
  

   Heraus 
  in 
  Hanau. 
  It 
  contained 
  as 
  much 
  iridium 
  as 
  could 
  be 
  

   alloyed 
  with 
  the 
  platinum 
  and 
  allow 
  of 
  its 
  being 
  properly 
  

   worked 
  — 
  about 
  20 
  per 
  cent. 
  The 
  length 
  was 
  \T^., 
  outside 
  

   diameter 
  ^r'^"' 
  and 
  the 
  thickness 
  of 
  the 
  wall 
  O-S"'"^ 
  It 
  was 
  made 
  

   from 
  three 
  pieces 
  of 
  sheet 
  metal, 
  the 
  main 
  cylinder 
  and 
  two 
  

   rounded 
  end 
  pieces, 
  welded 
  together 
  and 
  giving 
  of 
  course 
  a 
  

   seam 
  around 
  each 
  end 
  and 
  down 
  the 
  middle. 
  These 
  seams 
  

   were 
  afterward 
  protected 
  by 
  a 
  thick 
  layer 
  of 
  platinum, 
  melted 
  

   and 
  dropped 
  on 
  to 
  the 
  hot 
  bulb 
  — 
  it 
  then 
  proved 
  and 
  has 
  since 
  

   remained 
  perfectly 
  tight. 
  The 
  stem 
  where 
  it 
  was 
  welded 
  on 
  

   to 
  the 
  bulb 
  (welding 
  seam 
  also 
  strengthened 
  with 
  platinum) 
  

   was 
  also 
  made 
  of 
  the 
  20 
  per 
  cent 
  alloy 
  for 
  a 
  distance 
  of 
  some 
  

   lO^""^ 
  out 
  from 
  the 
  bulb, 
  where 
  it 
  was 
  reduced 
  to 
  5 
  per 
  cent 
  for 
  

   the 
  remaining 
  20''" 
  of 
  its 
  length. 
  The 
  5 
  per 
  cent 
  alloy 
  is 
  much 
  

   less 
  brittle 
  and, 
  therefore, 
  more 
  convenient 
  to 
  handle. 
  In 
  out- 
  

   side 
  diameter 
  the 
  stem 
  was 
  2'""' 
  and 
  inside 
  0*75'"™. 
  It 
  was 
  con- 
  

   nected 
  with 
  the 
  capillary 
  tube 
  leading 
  to 
  the 
  manometer 
  by 
  

   means 
  of 
  a 
  short 
  overlapping 
  glass 
  tube 
  sealed 
  at 
  both 
  ends 
  

   with 
  sealing 
  wax. 
  It 
  was 
  possible 
  by 
  carefully 
  heating 
  to 
  draw 
  

   the 
  sealing 
  wax 
  in 
  between 
  glass 
  and 
  platinum 
  until 
  the 
  entire 
  

   space 
  around 
  the 
  ends 
  of 
  the 
  two 
  capillaries 
  was 
  filled, 
  thereby 
  

   adding 
  as 
  little 
  as 
  possible 
  to 
  the 
  volume 
  of 
  the 
  "unheated 
  

   space." 
  

  

  *Teiidt, 
  Zeitschr. 
  f. 
  physikal, 
  Cliem., 
  xxvi, 
  143, 
  1898. 
  

  

  