﻿of 
  various 
  Substances 
  on 
  Solidification. 
  225 
  

  

  1. 
  Between 
  the 
  hours 
  1.50 
  and 
  2.45 
  but 
  one 
  caliper 
  measurement 
  

   was 
  made, 
  namely 
  at 
  2.15, 
  and 
  upon 
  this 
  one 
  measurement 
  both 
  the 
  

   existence 
  and 
  the 
  amount 
  of 
  this 
  anomalous 
  part 
  of 
  the 
  curve 
  depend. 
  

   An 
  error 
  in 
  this 
  single 
  caliper 
  measurement 
  amounting 
  to 
  0-006 
  of 
  an 
  

   inch 
  was 
  sufficient 
  to 
  have 
  produced 
  it 
  ; 
  and 
  as 
  the 
  limit 
  of 
  reading 
  of 
  

   the 
  beam 
  calipers 
  was 
  to 
  a 
  limit 
  of 
  0*002 
  or 
  possibly 
  0*001 
  of 
  an 
  inch, 
  

   a 
  mistake 
  in 
  the 
  measurement 
  at 
  2.15, 
  or 
  a 
  misreading 
  of 
  only 
  the 
  decimal 
  

   •004 
  or 
  *005 
  at 
  most, 
  is 
  sufficient 
  to 
  account 
  for 
  the 
  anomaly. 
  

  

  2. 
  The 
  hump 
  on 
  the 
  curve 
  does 
  not 
  necessarily 
  indicate 
  expansion, 
  and 
  

   from 
  the 
  early 
  time 
  of 
  its 
  occurrence, 
  viz. 
  only 
  1 
  hour 
  25 
  minutes 
  from 
  

   the 
  commencement 
  of 
  cooling, 
  it 
  seems 
  highly 
  improbable 
  that 
  it 
  could 
  

   arise 
  from 
  partial 
  expansion 
  then 
  commencing, 
  while 
  as 
  yet 
  a 
  very 
  large 
  

   proportion 
  of 
  the 
  entire 
  mass 
  must 
  have 
  been 
  still 
  liquid. 
  

  

  3. 
  If 
  this 
  anomalous 
  part 
  of 
  the 
  curve 
  were 
  really 
  due 
  to 
  expansion, 
  it 
  

   must 
  have 
  much 
  more 
  extensively 
  affected 
  the 
  lower 
  prolongation 
  of 
  the 
  

   curve, 
  and 
  have 
  shown 
  itself 
  there 
  in 
  a 
  form 
  that 
  would 
  have 
  unmistakably 
  

   declared 
  its 
  origin. 
  

  

  4. 
  On 
  examining 
  the 
  curve 
  fig. 
  5 
  a 
  slight 
  anomaly 
  may 
  be 
  remarked 
  

   in 
  the 
  rate 
  of 
  contraction 
  of 
  the 
  empty 
  shell, 
  due 
  no 
  doubt 
  to 
  some 
  

   slight 
  error 
  in 
  the 
  third 
  measurement, 
  or 
  that 
  at 
  1.50 
  p.m. 
  In 
  this 
  in- 
  

   stance 
  it 
  would 
  be 
  impossible 
  to 
  ascribe 
  the 
  anomaly 
  to 
  expansion 
  of 
  any 
  

   sort. 
  

  

  The 
  dotted 
  line 
  A 
  (fig. 
  4) 
  may 
  therefore 
  be 
  viewed 
  as 
  completing 
  the 
  

   curve 
  of 
  contraction. 
  

  

  The 
  curve 
  fig. 
  6, 
  representing 
  the 
  volume 
  of 
  the 
  filled 
  shell 
  at 
  successive 
  

   epochs 
  of 
  cooling, 
  is 
  deduced 
  from 
  the 
  Table 
  (p. 
  221), 
  assuming 
  the 
  suc- 
  

   cessive 
  volumes 
  to 
  be 
  proportionate 
  to 
  the 
  cubes 
  of 
  the 
  diametric 
  measure- 
  

   ments, 
  the 
  curve 
  being 
  a 
  mean 
  drawn 
  through 
  the 
  several 
  points 
  of 
  

   observation.] 
  

  

  The 
  supposition 
  upon 
  which 
  Messrs. 
  Nasmyth 
  and 
  Carpenter's 
  theory 
  

   rests 
  may 
  be 
  divided 
  into 
  two 
  distinct 
  propositions. 
  

  

  1st. 
  That 
  cast 
  iron 
  is 
  of 
  greater 
  density 
  in 
  the 
  molten 
  than 
  in 
  the 
  solid 
  

   state. 
  

  

  2nd. 
  That 
  cast 
  iron 
  in 
  the 
  act 
  of 
  consolidation 
  expands 
  in 
  volume. 
  

   These 
  propositions 
  are 
  not 
  identical, 
  although 
  the 
  second 
  is 
  involved 
  in 
  

   the 
  first. 
  The 
  first 
  proposition 
  has 
  been 
  already 
  disposed 
  of, 
  and 
  the 
  

   last 
  recorded 
  experiments 
  appear 
  conclusively 
  to 
  disprove 
  the 
  second. 
  

  

  The 
  phenomena 
  described 
  by 
  Messrs. 
  Nasmyth 
  and 
  Carpenter, 
  and 
  

   their 
  explanation 
  of 
  the 
  circulating 
  currents 
  observable 
  in 
  large 
  and 
  nearly 
  

   cylindrical 
  ladles 
  of 
  molten 
  iron, 
  appear 
  at 
  first 
  sight 
  so 
  confirmatory 
  of 
  

   their 
  views 
  as 
  to 
  the 
  greater 
  density 
  of 
  cast 
  iron 
  in 
  the 
  molten 
  than 
  in 
  

   the 
  solid 
  state, 
  that 
  it 
  seems 
  necessary 
  here 
  to 
  present 
  the 
  true 
  explana- 
  

   tion 
  of 
  the 
  facts, 
  which, 
  so 
  far 
  as 
  they 
  are 
  here 
  relevant, 
  may 
  be 
  best 
  

   given 
  briefly 
  in 
  the 
  words 
  of 
  these 
  authors 
  : 
  — 
  

  

  " 
  When 
  a 
  ladle 
  of 
  molten 
  iron 
  is 
  drawn 
  from 
  the 
  furnace 
  and 
  allowed 
  

  

  