﻿of 
  various 
  Substances 
  on 
  Solidification. 
  

  

  223 
  

  

  the 
  shell 
  is 
  thinner*. 
  On 
  inspecting 
  the 
  Table 
  and 
  curve 
  fig. 
  5, 
  it 
  will 
  

   be 
  seen 
  that 
  the 
  empty 
  shell 
  had 
  its 
  diameter 
  thus 
  permanently 
  enlarged 
  

   by 
  0-008 
  of 
  an 
  inch 
  ; 
  and 
  had 
  it 
  been 
  heated 
  to 
  as 
  high 
  a 
  temperature 
  as 
  the 
  

   filled 
  shell, 
  we 
  may 
  allowably 
  conclude 
  that 
  this 
  enlargement 
  would 
  have 
  

   reached 
  0*01 
  of 
  an 
  inch. 
  The 
  filled 
  shell 
  has 
  had 
  its 
  diameter 
  increased 
  

   by 
  the 
  decimal 
  0"-ll 
  ; 
  and 
  if 
  we 
  deduct 
  from 
  this 
  the 
  amount 
  of 
  perma- 
  

   nent 
  enlargement 
  due 
  to 
  heating 
  only, 
  equal 
  to 
  that 
  of 
  the 
  empty 
  shell, 
  

   we 
  have 
  the 
  decimal 
  0-11 
  — 
  0*01 
  = 
  0-10, 
  which 
  has 
  to 
  be 
  otherwise 
  ac- 
  

   counted 
  for. 
  This 
  shell 
  was 
  at 
  a 
  bright 
  red 
  heat 
  visible 
  in 
  clear 
  daylight 
  

   when 
  filled 
  with 
  the 
  liquid 
  iron, 
  which 
  occupied 
  the 
  spherical 
  cavity 
  and 
  

   about 
  0-43 
  in 
  height 
  of 
  that 
  of 
  the 
  fuse-hole. 
  The 
  temperature 
  of 
  the 
  

   shell 
  visibly 
  rose 
  by 
  the 
  heat 
  communicated 
  from 
  the 
  liquid 
  metal, 
  and 
  in 
  

   30 
  minutes 
  after 
  it 
  was 
  filled 
  had 
  attained 
  its 
  maximum, 
  the 
  surface 
  being 
  

   then 
  at 
  a 
  bright 
  yellow 
  heat 
  in 
  daylight 
  when 
  the 
  first 
  measurement 
  of 
  

   enlarged 
  diameter 
  was 
  made. 
  The 
  successive 
  measurements 
  were 
  taken 
  

   for 
  orthogonal 
  diameters 
  in 
  the 
  direction 
  normal 
  to 
  the 
  fuse-hole 
  by 
  

   means 
  of 
  finely 
  graduated 
  steel 
  beam 
  calipers 
  capable 
  of 
  being 
  read 
  to 
  

   0*002 
  of 
  an 
  inch 
  or 
  even 
  less 
  ; 
  the 
  dimensions 
  set 
  down 
  in 
  the 
  Table 
  are 
  

   the 
  means 
  of 
  each 
  pair 
  of 
  orthogonal 
  diameters. 
  The 
  shell 
  was 
  thus 
  

   heated 
  at 
  the 
  commencement, 
  and 
  before 
  consolidation 
  of 
  its 
  liquid 
  con- 
  

   tents 
  had 
  taken 
  place 
  to 
  any 
  considerable 
  extent, 
  to 
  within 
  probably 
  200° 
  

   or 
  300° 
  Fahr. 
  of 
  the 
  temperature 
  of 
  the 
  cast 
  iron 
  within. 
  The 
  shell 
  and 
  

   its 
  contents 
  are 
  therefore 
  at 
  the 
  commencement 
  very 
  nearly 
  in 
  the 
  same 
  

   condition 
  as 
  though 
  the 
  whole 
  were 
  a 
  sphere 
  of 
  molten 
  iron 
  without 
  any 
  

   more 
  or 
  less 
  rigid 
  envelope, 
  if 
  such 
  could 
  exist. 
  Reverting 
  to 
  what 
  has 
  

   been 
  said 
  above 
  as 
  to 
  the 
  train 
  of 
  forces 
  called 
  into 
  play 
  in 
  a 
  cooling 
  

   sphere, 
  let 
  us 
  consider 
  what 
  has 
  taken 
  place 
  here. 
  As 
  the 
  heat 
  is 
  dissi- 
  

   pated 
  from 
  the 
  exterior 
  of 
  the 
  molten 
  mass, 
  being 
  transmitted 
  through 
  

   the 
  shell, 
  omTcouche 
  after 
  another 
  of 
  the 
  molten 
  metal 
  in 
  contact 
  with 
  

   the 
  inner 
  wall 
  of 
  the 
  shell 
  consolidates, 
  the 
  thickness 
  constantly 
  advan- 
  

   cing 
  towards 
  the 
  interior, 
  where 
  the 
  metal 
  is 
  still 
  liquid. 
  If 
  each 
  of 
  these 
  

   couches 
  in 
  consolidating 
  expanded 
  in 
  volume, 
  such 
  expansion 
  must 
  con- 
  

   spire, 
  with 
  the 
  contraction 
  constantly 
  going 
  on 
  by 
  the 
  abasement 
  of 
  tem- 
  

   perature, 
  to 
  produce 
  compression 
  in 
  the 
  central 
  and 
  as 
  yet 
  unsolidified 
  

   portion 
  of 
  the 
  mass. 
  If, 
  on 
  the 
  contrary, 
  each 
  couche 
  as 
  it 
  solidifies 
  con- 
  

   tracts 
  in 
  volume 
  (and, 
  as 
  is 
  the 
  fact, 
  by 
  a 
  larger 
  coefficient 
  of 
  contraction 
  

   for 
  equal 
  small 
  ranges 
  of 
  temperature 
  before 
  and 
  after 
  solidification), 
  then 
  

   the 
  effect 
  must 
  be 
  that, 
  after 
  the 
  solidified 
  crust 
  has 
  attained 
  a 
  certain 
  

   thickness 
  and 
  sufficient 
  rigidity, 
  the 
  further 
  progress 
  of 
  contraction 
  of 
  

   the 
  central 
  portions 
  as 
  they 
  successively 
  solidify 
  must 
  be 
  met 
  by 
  their 
  

   tending 
  to 
  draw 
  off 
  from 
  the 
  solidified 
  shell, 
  or, 
  in 
  other 
  words, 
  by 
  a 
  

   drawing-off 
  from 
  each 
  other 
  of 
  the 
  particles 
  of 
  that 
  central 
  portion 
  of 
  

   * 
  For 
  a 
  more"complete~analysis~of 
  the 
  complex 
  strains 
  brought 
  into 
  play 
  by 
  expan- 
  

   sion 
  and 
  contraction 
  in 
  the 
  heating 
  and 
  cooling 
  of 
  metallic 
  solids 
  of 
  revolution, 
  the 
  

   author 
  may 
  refer 
  to 
  his 
  paper 
  " 
  On 
  the 
  Coefficients 
  T 
  e 
  and 
  T 
  r 
  in 
  large 
  masses 
  of 
  Forged 
  

   Iron," 
  published 
  in 
  the 
  Minutes 
  of 
  Proceedings 
  Inst. 
  C. 
  E. 
  London, 
  vol. 
  xviii. 
  p. 
  299. 
  

  

  