﻿1875.] 
  

  

  On 
  certain 
  Alloys 
  of 
  Silver 
  and 
  Cupper. 
  

  

  319 
  

  

  was 
  broken 
  up 
  and 
  disappeared, 
  leaving 
  a 
  continuous 
  channelled-space 
  

   spectrum. 
  

  

  These 
  experiments, 
  made 
  at 
  the 
  Royal 
  Mint, 
  were 
  often 
  prolonged 
  for 
  

   many 
  hours 
  consecutively. 
  They 
  involved 
  much 
  furnace-work 
  of 
  a 
  pecu- 
  

   liarly 
  trying 
  nature 
  ; 
  and 
  we 
  have 
  much 
  pleasure 
  in 
  acknowledging 
  

   the 
  assistance 
  we 
  received 
  from 
  Mr. 
  Edward 
  Rigg, 
  one 
  of 
  the 
  assistant 
  

   assayers, 
  who 
  conducted 
  many 
  of 
  the 
  tedious 
  manipulations 
  with 
  great 
  

   skill 
  and 
  patience. 
  We 
  should 
  also 
  mention 
  that 
  the 
  care 
  exercised 
  by 
  

   Joseph 
  Groves, 
  senior 
  fireman, 
  in 
  the 
  preparation 
  of 
  the 
  furnace 
  and 
  the 
  

   lime-moulds, 
  contributed 
  in 
  no 
  small 
  measure 
  to 
  the 
  success 
  of 
  the 
  

   experiments 
  . 
  

  

  It 
  appears 
  to 
  us 
  that 
  these 
  experiments, 
  conducted 
  at 
  the 
  high 
  tem- 
  

   perature 
  of 
  the 
  oxyhydrogen 
  flame, 
  go 
  far 
  to 
  support 
  the 
  conclusions 
  

   which 
  were 
  drawn 
  from 
  the 
  experiments 
  at 
  a 
  lower 
  temperature. 
  First, 
  

   in 
  passing 
  from 
  the 
  liquid 
  to 
  the 
  most 
  perfect 
  gaseous 
  state, 
  vapours 
  are 
  

   composed 
  of 
  molecules 
  of 
  different 
  orders 
  of 
  complexity 
  ; 
  and 
  second, 
  

   this 
  complexity 
  is 
  diminished 
  by 
  the 
  dissociating 
  action 
  of 
  heat, 
  each 
  

   molecular 
  simplification 
  being 
  marked 
  by 
  a 
  distinctive 
  spectrum. 
  There 
  

   is 
  also 
  an 
  intimate 
  connexion 
  between 
  the 
  facility 
  with 
  which 
  the 
  final 
  

   stage 
  is 
  reached, 
  the 
  group 
  to 
  which 
  the 
  element 
  belongs, 
  and 
  the 
  place 
  

   which 
  it 
  occupies 
  in 
  the 
  solar 
  atmosphere. 
  

  

  III. 
  " 
  On 
  the 
  Liquation, 
  Fusibility, 
  and 
  Density 
  of 
  certain 
  Alloys 
  

   of 
  Silver 
  and 
  Copper." 
  By 
  W. 
  Chandler 
  Roberts, 
  Chemist 
  

   of 
  the 
  Mint. 
  Communicated 
  by 
  Dr. 
  Percy, 
  F.R.S. 
  Received 
  

   March 
  11, 
  1875. 
  

  

  (Abstract.) 
  

  

  The 
  author 
  states 
  that 
  the 
  most 
  remarkable 
  physical 
  property 
  of 
  silver- 
  

   copper 
  alloys 
  is 
  a 
  molecular 
  mobility, 
  in 
  virtue 
  of 
  which 
  certain 
  combina- 
  

   tions 
  of 
  the 
  constituents 
  of 
  a 
  molten 
  alloy 
  become 
  segregated 
  from 
  the 
  

   mass, 
  the 
  homogeneous 
  character 
  of 
  which 
  is 
  thereby 
  destroyed. 
  These 
  

   irregularities 
  of 
  composition 
  have 
  long 
  been 
  known, 
  and 
  reference 
  is 
  

   made 
  to 
  them 
  in 
  the 
  works 
  of 
  Lazarus 
  Erckern 
  (1650) 
  and 
  of 
  Jars 
  

   (1774). 
  A 
  very 
  complete 
  memoir 
  was 
  published 
  in 
  1852 
  by 
  Levol, 
  who 
  

   did 
  much 
  towards 
  ascertaining 
  the 
  nature 
  and 
  defining 
  the 
  hmits 
  of 
  this 
  

   molecular 
  mobility. 
  He 
  discovered 
  the 
  important 
  fact 
  that 
  an 
  alloy 
  con- 
  

   taining 
  71'89 
  per 
  cent, 
  of 
  silver 
  is 
  uniform 
  in 
  composition. 
  Its 
  chemical 
  

   formula 
  (Ag 
  3 
  Cu 
  2 
  ) 
  and 
  peculiar 
  structure 
  led 
  him 
  to 
  conclude 
  that 
  all 
  

   other 
  alloys 
  are 
  mixtures 
  of 
  this, 
  with 
  excess 
  of 
  either 
  metal. 
  

  

  The 
  electric 
  conductivity 
  of 
  these 
  alloys 
  was 
  studied 
  in 
  1860 
  by 
  Mat- 
  

   thiessen, 
  who 
  doubted 
  the 
  accuracy 
  of 
  Levol's 
  theory, 
  and 
  viewed 
  them 
  

   as 
  " 
  mechanical 
  mixtures 
  of 
  allotropic 
  modifications 
  of 
  the 
  two 
  metals 
  in 
  

   each 
  other." 
  

  

  