﻿1875.] 
  On 
  the 
  Liquation 
  of 
  Alloys 
  of 
  Silver 
  and 
  Copper. 
  433 
  

  

  I. 
  u 
  On 
  the 
  Liquation 
  of 
  Alloys 
  of 
  Silver 
  and 
  Copper/" 
  In 
  a 
  Letter 
  

   addressed 
  to 
  the 
  Secretaries 
  of 
  the 
  Royal 
  Society, 
  by 
  Col. 
  

   J. 
  T. 
  Smith, 
  Madras 
  Engineers, 
  F.R.S. 
  Received 
  April 
  2, 
  

   1875. 
  

  

  It 
  has 
  occurred 
  to 
  me 
  that 
  it 
  might 
  be 
  useful, 
  as 
  a 
  guide 
  to 
  future 
  

   inquiries, 
  if 
  I 
  were 
  to 
  communicate, 
  in 
  reference 
  to 
  Mr, 
  Roberts's 
  

   paper 
  " 
  On 
  the 
  Liquation, 
  Fusibility, 
  and 
  Density 
  of 
  certain 
  Alloys 
  of 
  

   Silver 
  and 
  Copper," 
  the 
  results 
  of 
  some 
  experiments 
  made 
  by 
  me 
  many 
  

   years 
  ago, 
  the 
  cod 
  elusion 
  to 
  which 
  I 
  was 
  led 
  being 
  that 
  the 
  separation 
  

   of 
  the 
  constituent 
  parts 
  of 
  an 
  alloy 
  coutaining 
  91| 
  per 
  cent, 
  of 
  silver 
  

   was 
  not 
  so 
  much 
  due 
  to 
  the 
  rapidity 
  or 
  slowness 
  with 
  which 
  the 
  heat 
  of 
  

   the 
  fluid 
  metal 
  was 
  abstracted, 
  as 
  to 
  the 
  inequality 
  affecting 
  its 
  removal 
  

   from 
  the 
  different 
  parts 
  of 
  the 
  melted 
  mass 
  in 
  the 
  act 
  of 
  consolidation. 
  

   Thus, 
  if 
  a 
  crucible 
  full 
  of 
  the 
  melted 
  alloy 
  were 
  lifted 
  out 
  of 
  the 
  furnace 
  

   and 
  placed 
  on 
  the 
  floor 
  to 
  cool, 
  the 
  surface 
  of 
  the 
  melted 
  metal 
  within 
  it 
  

   being 
  well 
  covered 
  with 
  a 
  thick 
  layer 
  of 
  hot 
  ashes, 
  the 
  lower 
  parts 
  of 
  

   the 
  mass, 
  after 
  it 
  had 
  become 
  solid, 
  would 
  be 
  found 
  to 
  contain 
  less 
  silver 
  

   in 
  proportion 
  than 
  the 
  upper 
  surface. 
  

  

  If, 
  on 
  the 
  other 
  hand, 
  the 
  crucible 
  were 
  left 
  to 
  cool 
  while 
  imbedded 
  in 
  

   the 
  furnace, 
  the 
  upper 
  surface 
  only 
  being 
  exposed 
  to 
  the 
  air, 
  except 
  a 
  

   thin 
  layer 
  to 
  protect 
  it 
  from 
  oxidation, 
  then 
  the 
  lower 
  parts 
  would, 
  after 
  

   solidification, 
  be 
  found 
  finer 
  than 
  the 
  upper 
  surface. 
  

  

  The 
  variations 
  here 
  referred 
  to 
  are 
  not 
  considerable 
  ; 
  but 
  they 
  some- 
  

   times 
  become 
  of 
  practical 
  importance, 
  especially 
  in 
  those 
  cases 
  wherein, 
  

   as 
  the 
  practice 
  of 
  the 
  Indian 
  Mints 
  used 
  to 
  be, 
  the 
  value 
  of 
  a 
  large 
  mass 
  

   of 
  coins 
  is 
  calculated 
  by 
  the 
  assay 
  of 
  samples 
  cut 
  from 
  a 
  representative 
  

   bar, 
  formed 
  by 
  melting 
  together 
  a 
  number 
  of 
  the 
  pieces 
  selected 
  from 
  the 
  

   mass. 
  

  

  Under 
  certain 
  conditions, 
  different 
  parts 
  of 
  a 
  bar 
  of 
  50 
  or 
  60 
  lbs. 
  

   weight, 
  cast 
  horizontally, 
  though 
  composed 
  of 
  metal 
  which, 
  previous 
  to 
  

   being 
  poured 
  from 
  the 
  crucible, 
  was 
  perfectly 
  homogeneous, 
  might 
  be 
  

   found 
  to 
  vary 
  as 
  much 
  as 
  \\ 
  or 
  even 
  2 
  per 
  cent. 
  A 
  much 
  smaller 
  

   difference 
  than 
  this 
  might 
  be 
  the 
  cause 
  of 
  considerable 
  loss 
  or 
  gain 
  in 
  

   the 
  valuation 
  of 
  a 
  large 
  invoice. 
  

  

  This 
  peculiar 
  action 
  in 
  the 
  cooling 
  of 
  melted 
  silver 
  alloy 
  first 
  attracted 
  

   notice 
  by 
  observation 
  of 
  the 
  fact 
  that 
  coinage-ingots, 
  which 
  were 
  about 
  

   15 
  inches 
  high, 
  2| 
  inches 
  broad, 
  and 
  -J 
  inch 
  thick, 
  cast 
  in 
  vertical 
  iron 
  

   moulds, 
  were 
  uniformly 
  finer 
  at 
  their 
  upper 
  surface 
  and 
  coarser 
  at 
  their 
  

   sides 
  and 
  bottom, 
  especially 
  at 
  the 
  corners. 
  

  

  It 
  was 
  at 
  first 
  thought 
  possible 
  that 
  this 
  might 
  be 
  due 
  to 
  the 
  combus- 
  

   tion 
  of 
  the 
  oil 
  employed 
  to 
  lubricate 
  the 
  moulds 
  causing 
  a 
  sensible 
  

   refinement 
  of 
  the 
  metal, 
  as 
  the 
  flames 
  were 
  frequently 
  tinged 
  by 
  copper 
  ; 
  

   but 
  the 
  same 
  increased 
  fineness 
  of 
  the 
  tops 
  of 
  the 
  ingots 
  was 
  found 
  to 
  

   exist 
  when 
  they 
  had 
  been 
  poured 
  into 
  new 
  iron 
  moulds 
  which 
  had 
  never 
  

  

  2 
  m 
  2 
  

  

  