﻿1874.] 
  Coefficient 
  of 
  Expansion 
  of 
  a 
  Paraffine. 
  109 
  

  

  (37°*7o 
  C.) 
  it 
  begins 
  to 
  soften 
  slightly, 
  and 
  gradually 
  becomes 
  softer 
  as 
  

   the 
  temperature 
  rises, 
  until 
  just 
  before 
  reaching 
  the 
  f 
  using-point, 
  142° 
  F. 
  

   (61°-11 
  C), 
  it 
  is 
  quite 
  plastic, 
  and 
  may 
  be 
  moulded 
  by 
  pressure, 
  or 
  spread 
  

   out 
  into 
  thin 
  coherent 
  sheets. 
  It 
  thus 
  resembles 
  some 
  metals 
  which 
  are 
  

   brittle 
  at 
  the 
  ordinary 
  temperature, 
  but 
  become 
  more 
  and 
  more 
  malleable 
  

   as 
  the 
  temperature 
  rises. 
  As 
  the 
  temperature 
  rises, 
  the 
  paraffine 
  becomes 
  

   more 
  and 
  more 
  translucent 
  j 
  and, 
  like 
  sealing-wax 
  and 
  some 
  other 
  bodies, 
  

   it 
  becomes 
  what 
  we 
  may 
  call 
  either 
  semifluid 
  or 
  semisolid 
  before 
  it 
  

   finally 
  fuses 
  to 
  a 
  colourless 
  perfectly 
  transparent 
  fluid. 
  As 
  the 
  tempera- 
  

   ture 
  approaches 
  400° 
  F. 
  (205°- 
  5 
  C), 
  the 
  liquid 
  begins 
  to 
  give 
  off 
  fumes 
  ; 
  it 
  

   " 
  flashes 
  " 
  (that 
  is 
  to 
  say, 
  the 
  vapour 
  ignites 
  on 
  the 
  application 
  of 
  flame, 
  

   but 
  does 
  not 
  continue 
  to 
  burn) 
  at 
  458° 
  F. 
  (236 
  c 
  -65 
  C.) 
  ; 
  and 
  the 
  vapour 
  

   ignites 
  spontaneously 
  without 
  the 
  presence 
  of 
  flame 
  and 
  continues 
  to 
  burn 
  

   at 
  576° 
  F. 
  (302°*75 
  C). 
  Finally 
  the 
  boiling-point 
  is 
  above 
  the 
  melting- 
  

   point 
  of 
  lead 
  and 
  the 
  boiling-point 
  of 
  mercury, 
  but 
  below 
  the 
  melting- 
  

   point 
  of 
  zinc 
  (apparently 
  not 
  much 
  below 
  it), 
  presumably 
  about 
  750° 
  F. 
  

   (398°-8 
  C). 
  Air-thermometer 
  determinations 
  of 
  the 
  boiling-point 
  were 
  

   not 
  satisfactory. 
  As 
  the 
  liquid 
  cools 
  from 
  the 
  boiling-point 
  the 
  contrac- 
  

   tion 
  is 
  seen 
  to 
  be 
  enormous. 
  The 
  comparatively 
  small 
  quantity 
  of 
  liquid 
  

   paraffine 
  (about 
  15 
  grammes) 
  capable 
  of 
  being 
  contained 
  in 
  a 
  tube 
  15 
  

   centimetres 
  (nearly 
  6 
  inches) 
  long 
  by 
  15 
  millimetres 
  (nearly 
  § 
  inch) 
  

   diameter 
  can 
  be 
  seen 
  to 
  sink 
  two 
  or 
  three 
  centimetres 
  in 
  less 
  than 
  10 
  

   minutes. 
  The 
  subsidence 
  continues 
  until 
  the 
  point 
  of 
  solidification 
  is 
  

   attained, 
  when 
  the 
  mass 
  commences 
  to 
  solidify 
  at 
  the 
  bottom, 
  and 
  pro- 
  

   ceeds 
  gradually 
  up 
  the 
  sides 
  of 
  the 
  tube, 
  leaving 
  a 
  central 
  core 
  of 
  perfectly 
  

   fluid 
  matter 
  which 
  does 
  not 
  solidify 
  for 
  some 
  length 
  of 
  time. 
  The 
  mass 
  

   parts 
  with 
  its 
  heat 
  very 
  slowly. 
  When 
  perfectly 
  and 
  uniformly 
  cooled 
  

   down 
  to 
  the 
  ordinary 
  temperature, 
  a 
  hollow 
  central 
  core 
  is 
  found 
  in 
  the 
  

   mass 
  of 
  paraffine, 
  extending 
  nearly 
  to 
  the 
  bottom, 
  and 
  gradually 
  narrow- 
  

   ing 
  as 
  it 
  descends. 
  The 
  contraction 
  which 
  takes 
  place 
  in 
  passing 
  from 
  

   the 
  liquid 
  to 
  the 
  solid 
  condition 
  is 
  very 
  considerable. 
  

  

  The 
  expansion 
  which 
  paraffine 
  undergoes 
  when 
  heated 
  appeared 
  to 
  be 
  

   so 
  unusually 
  great, 
  that 
  the 
  following 
  experiments 
  were 
  made 
  in 
  order 
  to 
  

   determine 
  its 
  amount. 
  They 
  may 
  be 
  divided 
  into 
  three 
  parts, 
  viz. 
  ex- 
  

   periments 
  to 
  determine 
  : 
  — 
  (a) 
  the 
  coefficient 
  of 
  expansion 
  of 
  the 
  solid 
  

   for 
  temperatures 
  between 
  32° 
  F. 
  (0° 
  C.) 
  and 
  the 
  point 
  of 
  fusion, 
  142° 
  F. 
  

   (61°*11 
  C.) 
  ; 
  (/3) 
  the 
  precise 
  change 
  of 
  volume 
  which 
  ensues 
  when 
  the 
  solid 
  

   at 
  142° 
  F. 
  passes 
  into 
  the 
  liquid 
  at 
  142° 
  F. 
  ; 
  and 
  (y) 
  the 
  coefficient 
  of 
  ex- 
  

   pansion 
  of 
  the 
  liquid 
  between 
  its 
  point 
  of 
  maximum 
  density 
  (142° 
  F.) 
  and 
  

   its 
  boiling-point 
  (presumably 
  about 
  750° 
  F., 
  398°*8 
  C). 
  

  

  In 
  these 
  determinations 
  the 
  greatest 
  obstacle 
  to 
  be 
  contended 
  against 
  

   was 
  the 
  slight 
  conductivity 
  of 
  the 
  paraffine, 
  which 
  made 
  it 
  very 
  difficult 
  

   to 
  evenly 
  heat 
  either 
  a 
  solid 
  or 
  liquid 
  mass. 
  The 
  only 
  way 
  of 
  doing 
  this 
  

   was 
  to 
  keep 
  the 
  mass 
  for 
  a 
  length 
  of 
  time 
  at 
  the 
  precise 
  temperature 
  

   required 
  ; 
  and 
  this 
  it 
  is 
  almost 
  impossible 
  to 
  do 
  when 
  the 
  temperature 
  of 
  

  

  VOL. 
  XXIII. 
  K 
  

  

  