﻿232 
  Mr. 
  R. 
  Mallet 
  on 
  the 
  alleged 
  Expansion 
  

  

  volume 
  of 
  gaseous 
  matter 
  ininutely 
  diffused, 
  which 
  is 
  pretty 
  readily 
  sepa- 
  

   rated, 
  aud 
  is 
  characterized 
  by 
  a 
  white 
  vaporous 
  cloud 
  floating 
  thinly 
  over 
  

   the 
  issuing 
  stream 
  ; 
  if 
  the 
  slag 
  be 
  cooled 
  rapidly, 
  the 
  gaseous 
  or 
  vapori- 
  

   zable 
  bodies 
  present 
  become 
  confined 
  and 
  render 
  the 
  mass 
  vesicular, 
  while 
  

   if 
  cooled 
  more 
  slowly, 
  and 
  with 
  a 
  free 
  surface 
  for 
  the 
  escape 
  of 
  these, 
  

   the 
  mass 
  solidifies 
  more 
  solidly, 
  often 
  as 
  solidly 
  as 
  a 
  block 
  of 
  granite*. 
  

  

  Independently 
  of 
  the 
  buo}^ancy 
  that 
  is 
  produced 
  by 
  the 
  vesicularity 
  of 
  

   rapidly 
  cooled 
  slags, 
  it 
  is 
  highly 
  probable 
  that 
  relatively 
  cold 
  and 
  solid 
  

   slag, 
  whose 
  buoyancy 
  is 
  negative, 
  may 
  yet 
  float 
  on 
  molten 
  slag, 
  whose 
  

   density 
  is 
  less 
  than 
  its 
  own, 
  in 
  virtue 
  of 
  that 
  same 
  repellent 
  force 
  which, 
  

   as 
  we 
  have 
  seen, 
  acts 
  under 
  like 
  conditions 
  in 
  the 
  case 
  of 
  metals. 
  

  

  "With 
  respect 
  to 
  acid 
  silicates, 
  or 
  slags 
  analogous 
  to 
  glass 
  (which, 
  how- 
  

   ever, 
  are 
  not 
  referred 
  to 
  by 
  Messrs. 
  jNasinyth 
  and 
  Carpenter), 
  the 
  author 
  

   again 
  refers 
  to 
  the 
  results 
  given 
  in 
  his 
  paper 
  (Phil. 
  Trans. 
  1873). 
  These, 
  

   and 
  indeed 
  the 
  circumstances 
  attending 
  the 
  production 
  and 
  destruction 
  

   of 
  the 
  well-known 
  " 
  Eupert's 
  drops," 
  incontestably 
  prove 
  that 
  these 
  sili- 
  

   cates 
  also 
  are 
  less 
  dense 
  in 
  the 
  molten 
  than 
  in 
  the 
  solid 
  state, 
  and 
  that 
  

   they 
  contract 
  -violently 
  at 
  or 
  near 
  the 
  instant 
  of 
  consolidation. 
  

  

  The 
  author 
  has 
  more 
  than 
  once 
  heard 
  the 
  opinion 
  expressed 
  by 
  those 
  

   engaged 
  about 
  blast-furnaces, 
  that 
  their 
  slags 
  do 
  expand 
  in 
  consolidating, 
  

   based 
  upon 
  a 
  misinterpretation 
  of 
  the 
  following 
  frequently 
  occurring 
  cir- 
  

   cumstance 
  : 
  — 
  When 
  the 
  large 
  parallelopipeds 
  of 
  slag 
  (5 
  to 
  6 
  feet 
  square 
  by 
  

   2 
  to 
  3 
  feet 
  thick) 
  are 
  stripped 
  from 
  the 
  iron 
  square 
  frame 
  which 
  formed 
  

   their 
  edges, 
  and 
  are 
  being 
  removed'upon 
  the 
  iron 
  waggons 
  on 
  which 
  they 
  

   are 
  cast, 
  and 
  still, 
  as 
  often 
  happens, 
  in 
  a 
  very 
  hot 
  state, 
  or 
  even 
  with 
  a 
  

   still 
  liquid 
  or 
  viscous 
  interior, 
  though 
  rigid 
  externally, 
  it 
  occasionally 
  

   happens 
  that 
  such 
  a 
  block 
  

   bursts 
  asunder, 
  and 
  with 
  a 
  sud- 
  

   denness 
  which 
  is 
  sufficient 
  

   sometimes 
  to 
  scatter 
  danger- 
  

   ously 
  some 
  of 
  the 
  liquid 
  inte- 
  

   rior 
  ; 
  or 
  if 
  the 
  fracture 
  be 
  not 
  

   so 
  sudden, 
  and 
  the 
  interior 
  be 
  

   in 
  a 
  viscous 
  condition, 
  the 
  latter 
  

   may 
  continue 
  for 
  a 
  considerable 
  

   time 
  to 
  slowly 
  exude 
  in 
  fan- 
  

   tastic 
  shapes 
  from 
  any 
  aperture 
  

   of 
  escape 
  left 
  free 
  to 
  it 
  (see 
  

   fig. 
  9). 
  These 
  facts 
  have 
  been 
  

   supposed 
  to 
  indicate 
  that 
  the 
  

   interior 
  of 
  the 
  mass 
  expands 
  ^ 
  Tail 
  of 
  yet 
  viscid 
  slag 
  extruding 
  from 
  interior. 
  

  

  in 
  consolidating. 
  It 
  is 
  scarcely 
  necessary 
  here, 
  however, 
  to 
  enter 
  

  

  * 
  All 
  this 
  may 
  be 
  well 
  observed 
  in 
  the 
  millions 
  of 
  blocks 
  of 
  slag 
  from 
  the 
  Cleveland 
  

   blast-furnaces 
  of 
  which 
  the 
  vast 
  embankments 
  and 
  breakwater 
  at 
  the 
  estuary 
  of 
  the 
  

   Biver 
  Tees 
  have 
  been 
  formed. 
  

  

  