﻿certain 
  Alloys 
  of 
  Silver 
  and 
  Copper. 
  

  

  493 
  

  

  silver. 
  Fig. 
  6 
  shows 
  the 
  results 
  of 
  analyses 
  on 
  the 
  different 
  portions 
  of 
  

   a 
  mass 
  of 
  the 
  alloy 
  containing 
  333*3 
  parts 
  of 
  silver 
  per 
  thousand 
  (Ag 
  Cu 
  4 
  ). 
  

   The 
  mass 
  varies 
  in 
  composition, 
  but 
  the 
  arrangement 
  does 
  not 
  appear 
  to 
  

   have 
  been 
  guided 
  by 
  any 
  law. 
  

  

  The 
  inquiry 
  appears 
  to 
  show 
  that 
  several 
  alloys 
  of 
  silver 
  and 
  copper 
  

   are, 
  under 
  suitable 
  conditions, 
  as 
  homogeneous 
  as 
  Levol's 
  alloy, 
  the 
  chief 
  

   peculiarity 
  of 
  which 
  consists 
  in 
  its 
  not 
  being 
  liable 
  to 
  liquation 
  when 
  poured 
  

   into 
  a 
  mould 
  at 
  the 
  ordinary 
  temperature 
  and 
  cooled 
  rapidly. 
  

  

  It 
  will 
  be 
  remembered 
  that 
  experiments 
  prove 
  that 
  in 
  all 
  alloys 
  which 
  

   contain 
  less 
  than 
  71'89 
  per 
  cent, 
  of 
  silver 
  the 
  external 
  parts 
  are 
  richer 
  

   than 
  the 
  centre. 
  The 
  curve 
  of 
  fusibility 
  shows 
  that 
  the 
  alloys 
  which 
  con- 
  

   tain 
  less 
  than 
  35 
  per 
  cent, 
  of 
  silver 
  have 
  higher 
  melting-points 
  than 
  

   other 
  alloys 
  of 
  silver 
  and 
  copper, 
  or 
  even 
  than 
  pure 
  silver. 
  It 
  would 
  not 
  

   appear, 
  therefore, 
  that 
  liquation 
  is 
  the 
  falling 
  out 
  of 
  the 
  least 
  fusible 
  

   alloy 
  present 
  in 
  a 
  mass 
  of 
  silver 
  and 
  copper 
  ; 
  for 
  if 
  it 
  were, 
  the 
  external 
  

   portions 
  of 
  the 
  alloys 
  would 
  in 
  all 
  cases 
  be 
  less 
  rich 
  in 
  silver 
  than 
  the 
  

   centre. 
  

  

  I 
  cannot 
  at 
  this 
  stage 
  of 
  the 
  inquiry 
  offer 
  a 
  complete 
  explanation 
  of 
  

   this 
  molecular 
  rearrangement 
  ; 
  but 
  I 
  venture 
  to 
  think 
  that 
  the 
  results 
  

   already 
  obtained 
  are 
  interesting. 
  They 
  show, 
  first, 
  that 
  the 
  same 
  alloys 
  

   are 
  situated 
  on 
  the 
  turning-points 
  of 
  the 
  curves 
  of 
  fusibility 
  and 
  electric 
  

   conductivity 
  ; 
  and 
  second, 
  that 
  the 
  arrangement 
  of 
  an 
  alloy 
  is 
  to 
  a 
  great 
  

   extent 
  dependent 
  on 
  the 
  rate 
  at 
  which 
  it 
  is 
  cooled. 
  

  

  In 
  accordance 
  with 
  a 
  suggestion 
  made 
  to 
  me 
  by 
  Mr. 
  E. 
  Mallet, 
  I 
  have 
  

   endeavoured 
  to 
  determine 
  the 
  relation 
  between 
  the 
  densities 
  of 
  silver 
  in 
  

   the 
  solid 
  and 
  the 
  molten 
  state. 
  I 
  adopted 
  the 
  method 
  which 
  he 
  devised 
  

   and 
  has 
  employed 
  in 
  the 
  determination 
  of 
  the 
  density 
  of 
  molten 
  cast 
  

   iron 
  *. 
  

  

  A 
  conical 
  vessel 
  of 
  best 
  thin 
  Low-Moor 
  plate 
  (1 
  millim. 
  thick), 
  about 
  

   16 
  centims. 
  in 
  height, 
  and 
  having 
  an 
  internal 
  volume 
  of 
  about 
  540 
  cub. 
  

   centims., 
  was 
  weighed, 
  first 
  empty, 
  and 
  subsequently 
  when 
  filled 
  with 
  

   distilled 
  water 
  at 
  a 
  known 
  temperature. 
  The 
  necessary 
  data 
  were 
  thus 
  

   afforded 
  for 
  accurately 
  determining 
  its 
  capacity 
  at 
  the 
  temperature 
  of 
  the 
  

   air. 
  Molten 
  silver 
  was 
  then 
  poured 
  into 
  it, 
  the 
  temperature 
  at 
  the 
  

   time 
  of 
  pouring 
  being 
  ascertained 
  by 
  the 
  calorimetric 
  method 
  already 
  

   described. 
  The 
  precautions, 
  as 
  regards 
  filling, 
  pointed 
  out 
  by 
  Mr. 
  Mallet 
  

   were 
  adopted 
  ; 
  and 
  as 
  soon 
  as 
  the 
  metal 
  was 
  quite 
  cold, 
  the 
  cone 
  with 
  its 
  

   contents 
  was 
  again 
  weighed. 
  

  

  The 
  surface 
  of 
  the 
  molten 
  metal 
  in 
  the 
  crucible 
  was 
  covered 
  with 
  char- 
  

   coal 
  ; 
  and 
  as 
  pure 
  silver, 
  when 
  in 
  a 
  liquid 
  state, 
  is 
  known 
  to 
  absorb 
  oxy- 
  

   gen 
  if 
  exposed 
  to 
  the 
  air, 
  the 
  cone 
  was 
  filled 
  with 
  an 
  atmosphere 
  of 
  

   coal-gas. 
  

  

  * 
  Proc. 
  Eoy. 
  Soc. 
  vol. 
  xxii. 
  p. 
  366, 
  and 
  vol. 
  xxiii. 
  p. 
  209. 
  

  

  