﻿of 
  various 
  Substances 
  on 
  Solidification. 
  

  

  217 
  

  

  These 
  preliminary 
  explanations 
  will 
  enable 
  us 
  better 
  to 
  interpret 
  the 
  

   following 
  experiments. 
  

  

  Experiment 
  1. 
  An 
  irregular 
  piece, 
  believed 
  to 
  be 
  of 
  hard 
  and 
  dense 
  

   cast 
  iron, 
  and 
  also 
  a 
  ball 
  of 
  about 
  2\ 
  in. 
  diameter, 
  believed 
  to 
  be 
  of 
  close- 
  

   grained 
  grey 
  iron 
  : 
  both 
  sunk 
  to 
  the 
  bottom 
  when 
  thrown 
  into 
  the 
  ladle 
  

   of 
  liquid 
  iron, 
  and 
  remained 
  for 
  some 
  time 
  at 
  the 
  bottom 
  ; 
  both, 
  however, 
  

   reappeared 
  upon 
  the 
  surface 
  when 
  they 
  had 
  acquired 
  a 
  temperature 
  suffi- 
  

   cient 
  to 
  have 
  fused 
  off 
  portions 
  of 
  their 
  respective 
  masses. 
  

  

  [In 
  every 
  fresh-lined 
  ladle 
  of 
  liquid 
  cast 
  iron 
  there 
  are 
  circumferential 
  

   ascending 
  and 
  central 
  descending 
  currents 
  in 
  the 
  metal, 
  produced 
  by 
  the 
  

   gases 
  evolved 
  from 
  the 
  lining, 
  as 
  hereafter 
  fully 
  explained. 
  It 
  is 
  no 
  doubt 
  

   chiefly 
  to 
  these 
  ascending 
  currents 
  that 
  the 
  heated 
  ball 
  in 
  Experiment 
  1 
  

   owed 
  its 
  ascent 
  to 
  the 
  surface 
  ; 
  for 
  if 
  the 
  heating 
  took 
  place 
  in 
  perfectly 
  

   motionless 
  cast 
  iron, 
  there 
  seems 
  no 
  reason 
  why 
  the 
  place 
  of 
  the 
  sunken 
  

   ball 
  should 
  change 
  up 
  to 
  the 
  moment 
  of 
  complete 
  fusion*.] 
  

  

  Experiment 
  2. 
  Two 
  parallelopipeds, 
  each 
  2" 
  x 
  2" 
  x 
  6", 
  were 
  cast 
  of 
  close 
  

   grey 
  iron 
  ; 
  one 
  of 
  these 
  was 
  placed 
  cold 
  upon 
  the 
  surface 
  of 
  a 
  large 
  ladle 
  

   of 
  liquid 
  iron 
  of 
  like 
  quality 
  ; 
  the 
  other 
  was 
  heated 
  as 
  hot 
  as 
  it 
  would 
  

   bear 
  without 
  distortion, 
  viz. 
  to 
  nearly 
  a 
  bright 
  yellow 
  heat, 
  in 
  a 
  forge-fire, 
  

   and 
  then 
  placed 
  upon 
  the 
  surface 
  of 
  the 
  liquid 
  metal. 
  Both 
  pieces 
  floated, 
  

   and, 
  as 
  nearly 
  as 
  could 
  be 
  judged, 
  both 
  to 
  the 
  same 
  height 
  above 
  the 
  

   liquid, 
  namely 
  0*1808 
  in. 
  The 
  volume 
  of 
  the 
  cold 
  piece 
  being 
  24 
  cubic 
  

   inches, 
  the 
  ratio 
  of 
  the 
  immersed 
  to 
  the 
  emergent 
  portions 
  was 
  as 
  9*6 
  to 
  

   1, 
  the 
  effective 
  surface 
  upon 
  which 
  the 
  repulsive 
  force 
  could 
  act 
  in 
  pro- 
  

   ducing 
  floatation 
  being 
  12 
  sq. 
  in. 
  Assuming 
  that 
  the 
  heated 
  piece 
  has 
  

   been 
  raised 
  from 
  60° 
  Fahr. 
  (the 
  temperature 
  of 
  the 
  cold 
  piece) 
  to 
  2000° 
  

   Fahr., 
  and 
  applying 
  the 
  mean 
  coefficient 
  of 
  cubic 
  dilatation 
  as 
  above 
  given 
  

   to 
  this 
  range 
  of 
  temperature, 
  viz. 
  2000°- 
  60° 
  = 
  1940° 
  Fahr., 
  we 
  find 
  that 
  

   its 
  volume 
  was 
  enlarged 
  to 
  24*75 
  cubic 
  inches, 
  or 
  =^ 
  °^ 
  ^ 
  ne 
  Y 
  °l 
  unie 
  

   when 
  cold 
  ; 
  and 
  taking 
  the 
  specific 
  gravity 
  of 
  the 
  cold 
  piece 
  to 
  have 
  been 
  

   7*17 
  (see 
  ante), 
  that 
  of 
  the 
  hot 
  piece 
  would 
  be 
  reduced 
  to 
  7*10 
  ; 
  the 
  effec- 
  

   tive 
  repellent 
  surface 
  was 
  slightly 
  enlarged 
  in 
  the 
  hot 
  piece, 
  and 
  the 
  im- 
  

   mersed 
  volume 
  was 
  to 
  the 
  emergent 
  volume 
  as 
  9*66 
  : 
  1. 
  The 
  buoyancy 
  

   of 
  the 
  heated 
  piece 
  had 
  been 
  increased, 
  or, 
  more 
  correctly, 
  its 
  negative 
  

   buoyancy 
  had 
  been 
  decreased, 
  as 
  compared 
  with 
  that 
  of 
  the 
  cold 
  piece, 
  but 
  

   yet 
  it 
  has 
  sunk 
  deeper 
  into 
  the 
  liquid 
  iron 
  in 
  proportion 
  to 
  their 
  re- 
  

   spective 
  volumes. 
  We 
  may 
  therefore 
  be 
  justified 
  in 
  concluding 
  that 
  the 
  

   repellent 
  force 
  which 
  kept 
  both 
  pieces 
  afloat 
  is 
  diminished 
  in 
  energy 
  in 
  

   some 
  proportion 
  as 
  the 
  difference 
  in 
  temperature 
  between 
  the 
  liquid 
  metal 
  

   and 
  the 
  piece 
  floating 
  upon 
  it 
  is 
  diminished, 
  and 
  that 
  where 
  the 
  liquid 
  

   and 
  the 
  floating 
  pieces 
  are 
  alike 
  in 
  quality 
  of 
  metal, 
  both 
  the 
  negative 
  

   buoyancy 
  and 
  the 
  repellent 
  force 
  must 
  both 
  disappear 
  at 
  the 
  instant 
  that 
  

   the 
  floating 
  piece 
  itself 
  becomes 
  liquid 
  by 
  heat 
  abstracted 
  from 
  the 
  molten 
  

   metal. 
  

  

  * 
  All 
  passages 
  printed 
  in 
  brackets 
  take 
  date 
  from 
  20th 
  December, 
  1874. 
  

  

  s2 
  

  

  