﻿[ 
  C31 
  ] 
  

  

  LXXI. 
  The 
  Thermal 
  Expansion 
  of 
  Porcelain. 
  

   By 
  A. 
  E. 
  Tutton, 
  B.Sc, 
  F.R.S* 
  

  

  rilHE 
  thermal 
  expansion 
  of 
  porcelain 
  has 
  formed 
  the 
  

   JL 
  subject 
  of 
  several 
  investigations 
  during 
  the 
  last 
  three 
  

   years, 
  and 
  has 
  become 
  a 
  subject 
  of 
  considerable 
  importance 
  

   in 
  consequence 
  of 
  the 
  employment 
  of 
  porcelain 
  of 
  the 
  Bayeux 
  

   and 
  Berlin 
  varieties 
  for 
  the 
  reservoirs 
  of 
  air-thermometers. 
  

  

  The 
  present 
  investigation 
  has 
  been 
  carried 
  out 
  with 
  a 
  spe- 
  

   cimen 
  of 
  Bayeux 
  porcelain, 
  which 
  was 
  kindly 
  placed 
  at 
  the 
  

   authors 
  disposal 
  by 
  Prof. 
  Calendar. 
  It 
  is 
  of 
  especial 
  interest 
  

   as 
  being 
  cut 
  from 
  the 
  same 
  tube 
  which 
  was 
  employed 
  (1 
  metre 
  

   length 
  of 
  it) 
  by 
  Bedford 
  in 
  an 
  investigation, 
  by 
  the 
  method 
  

   of 
  Callendar, 
  of 
  the 
  expansion 
  of 
  this 
  variety 
  of 
  porcelain 
  

   between 
  0° 
  and 
  830° 
  (Phil. 
  Mag. 
  vol. 
  xlix. 
  p. 
  90) 
  ; 
  and 
  of 
  

   which 
  same 
  tube 
  also 
  a 
  piece 
  was 
  used 
  by 
  Chappuis 
  in 
  a 
  

   series 
  of 
  determinations, 
  by 
  the 
  Fizeau 
  method, 
  for 
  the 
  

   interval 
  0° 
  to 
  83°. 
  It 
  was 
  the 
  fact 
  of 
  there 
  being 
  some 
  dis- 
  

   crepancy 
  between 
  the 
  results 
  of 
  these 
  observers 
  that 
  induced 
  

   Prof. 
  Callendar 
  to 
  suggest 
  to 
  the 
  author 
  the 
  carrying 
  out 
  of 
  

   an 
  independent 
  series 
  of 
  determinations, 
  with 
  the 
  delicate 
  

   interference-dilatometer 
  described 
  by 
  the 
  author 
  to 
  the 
  Royal 
  

   Society 
  in 
  the 
  year 
  1898 
  (Phil. 
  Trans. 
  A. 
  vol, 
  exci. 
  p. 
  313, 
  

   and 
  vol. 
  excii. 
  p. 
  455). 
  

  

  The 
  interference-dilatometer 
  in 
  question 
  possesses 
  all 
  the 
  

   advautages 
  over 
  the 
  original 
  Fizeau 
  apparatus 
  of 
  the 
  Bureau 
  

   International 
  des 
  Poids 
  et 
  Mesures, 
  Sevres, 
  of 
  that 
  devised 
  

   by 
  Abbe 
  and 
  elaborated 
  by 
  Pulfrich 
  (Zeitschr. 
  fitr 
  Instru- 
  

   mentenkunde, 
  1893, 
  p. 
  365); 
  together 
  with 
  further 
  improve- 
  

   ments 
  on 
  the 
  Abbe 
  form. 
  Two 
  of 
  these 
  improvements 
  are 
  

   of 
  considerable 
  importance, 
  namely, 
  the 
  separation 
  of 
  the 
  

   observing 
  part 
  of 
  the 
  apparatus 
  from 
  the 
  expansion-chamber, 
  

   and 
  its 
  removal 
  to 
  an 
  adequate 
  distance 
  from 
  the 
  heated 
  

   atmosphere 
  above 
  the 
  bath 
  in 
  which 
  the 
  latter 
  is 
  heated 
  ; 
  and 
  

   the 
  measurement 
  of 
  the 
  temperature 
  of 
  the 
  interference 
  tripod, 
  

   and 
  the 
  substance 
  under 
  investigation 
  which 
  it 
  carries, 
  by 
  

   means 
  of 
  a 
  thermometer 
  bent 
  just 
  above 
  the 
  cylindrical 
  bulb 
  

   and 
  so 
  arranged 
  that 
  the 
  latter 
  lies 
  on 
  the 
  platinum-iridium 
  

   tripod 
  table, 
  in 
  tied 
  contact 
  with 
  one 
  of 
  the 
  screws 
  supporting 
  

   the 
  glass 
  cover-disk, 
  and 
  only 
  a 
  millimetre 
  distant 
  from 
  the 
  

   substance 
  itself. 
  For 
  the 
  author 
  has 
  proved 
  by 
  direct 
  expe- 
  

   riment 
  that 
  a 
  thermometer 
  merely 
  hung 
  alongside 
  in 
  the 
  bath 
  

   docs 
  not 
  register 
  the 
  temperature 
  of 
  the 
  tripod, 
  which 
  at 
  the 
  

   higher 
  limit 
  of 
  120° 
  may 
  be 
  as 
  much 
  as 
  3° 
  lower. 
  The 
  chief 
  

  

  * 
  Communicated 
  by 
  the 
  Physical 
  Society: 
  read 
  March 
  14, 
  11)02. 
  

  

  