﻿104 
  

  

  Mr. 
  GL 
  F. 
  Rodwell 
  on 
  the 
  

  

  [Dec. 
  10, 
  

  

  it, 
  was 
  found 
  to 
  be 
  -047619 
  ; 
  hence 
  a 
  volume 
  of 
  amorphous 
  iodide 
  repre- 
  

   sented 
  by 
  unity 
  becomes 
  a 
  volume 
  of 
  1*047619 
  in 
  passing 
  into 
  the 
  crys- 
  

   talline 
  condition, 
  plus 
  the 
  intercrystalline 
  spaces 
  ; 
  and 
  the 
  volume 
  of 
  these 
  

   spaces 
  having 
  been 
  determined 
  above, 
  we 
  find 
  that 
  the 
  actual 
  change 
  of 
  

   volume 
  which 
  takes 
  place 
  simultaneously 
  with 
  the 
  change 
  of 
  molecular 
  

   condition 
  amounts 
  to 
  '011323 
  ; 
  that 
  is, 
  a 
  volume 
  of 
  iodide 
  at 
  its 
  point 
  

   of 
  maximum 
  density 
  (116° 
  C.) 
  represented 
  by 
  unity 
  becomes 
  a 
  volume 
  

   of 
  1-011323 
  in 
  changing 
  to 
  the 
  crystalline 
  condition. 
  

  

  Frequent 
  fusion 
  and 
  cooling 
  appear 
  to 
  render 
  a 
  mass 
  of 
  iodide 
  more 
  

   brittle 
  and 
  crystalline, 
  and 
  to 
  promote 
  the 
  formation 
  of 
  large 
  fissures. 
  

   The 
  iodide 
  prepared 
  by 
  dissolving 
  silver 
  in 
  hydriodic 
  acid 
  and 
  subsequent 
  

   fusion 
  was 
  less 
  brittle 
  than 
  that 
  produced 
  by 
  precipitation 
  and 
  fre- 
  

   quently 
  fused. 
  We 
  have 
  before 
  noticed 
  that 
  while 
  the 
  latter 
  passes 
  into 
  

   its 
  crystalline 
  condition 
  at 
  a 
  temperature 
  ranging 
  a 
  few 
  degrees 
  on 
  either 
  

   side 
  of 
  116° 
  C, 
  the 
  former 
  may 
  sometimes 
  be 
  cooled 
  to 
  much 
  lower 
  tem- 
  

   peratures 
  without 
  change 
  ; 
  in 
  fact 
  it 
  appears 
  to 
  be 
  altogether 
  more 
  com- 
  

   pact 
  and 
  horny 
  and 
  freer 
  from 
  intercrystalline 
  spaces 
  than 
  the 
  fused 
  iodide 
  

   produced 
  by 
  precipitation, 
  indeed 
  almost 
  perfectly 
  free. 
  The 
  specific 
  gra- 
  

   vity 
  appears 
  also 
  to 
  be 
  slightly 
  higher. 
  Boullay 
  found 
  the 
  specific 
  gravity 
  

   of 
  the 
  fused 
  iodide 
  produced 
  by 
  precipitation 
  to 
  be 
  5- 
  61 
  ; 
  but 
  he 
  was 
  probab]y 
  

   unaware 
  of 
  the 
  presence 
  of 
  the 
  intercrystalline 
  spaces, 
  or 
  he 
  did 
  not 
  

   take 
  special 
  precautions 
  to 
  obviate 
  them. 
  An 
  ordinary 
  fused 
  mass 
  of 
  

   iodide 
  was 
  found 
  to 
  have 
  a 
  specific 
  gravity 
  of 
  5*545, 
  when 
  no 
  precautions 
  

   were 
  taken 
  to 
  dislodge 
  the 
  air 
  from 
  the 
  intercrystalline 
  spaces. 
  Now 
  we 
  

   have 
  already 
  given 
  reasons 
  for 
  believing 
  that 
  a 
  volume 
  of 
  iodide 
  at 
  

   its 
  maximum 
  density 
  (116° 
  C.) 
  becomes 
  a 
  volume 
  of 
  1*047619 
  in 
  chang- 
  

   ing 
  to 
  the 
  crystalline 
  condition 
  ; 
  and 
  if 
  we 
  take 
  the 
  specific 
  gravity 
  to 
  be 
  

   5*816 
  at 
  the 
  maximum 
  density, 
  we 
  deduce 
  the 
  specific 
  gravity 
  in 
  the 
  

   crystalline 
  condition, 
  not 
  taking 
  into 
  account 
  the 
  intercrystalline 
  spaces, 
  

   to 
  be 
  5*561, 
  

  

  1*0476 
  : 
  1 
  : 
  : 
  5*816 
  : 
  5*561, 
  

  

  a 
  number 
  which 
  differs 
  by 
  only 
  0*016 
  from 
  the 
  specific 
  gravity 
  found 
  by 
  

   direct 
  weighing, 
  when 
  no 
  precautions 
  were 
  taken 
  to 
  dislodge 
  air 
  from 
  the 
  

   intercrystalline 
  spaces. 
  "When, 
  however, 
  the 
  mass 
  of 
  iodide 
  was 
  boiled 
  

   for 
  a 
  length 
  of 
  time 
  in 
  water 
  and 
  cooled 
  in 
  a 
  good 
  vacuum, 
  the 
  specific 
  

   gravity 
  at 
  0° 
  C. 
  was 
  found 
  to 
  be 
  5*681. 
  Deville 
  found 
  it 
  under 
  the 
  same 
  

   conditions 
  to 
  be 
  5*687*^ 
  The 
  specific 
  gravity 
  of 
  the 
  molten 
  iodide 
  has 
  

   been 
  shown 
  above 
  to 
  be 
  about 
  5*406, 
  and 
  the 
  specific 
  gravity 
  at 
  the 
  point 
  

   of 
  maximum 
  density 
  of 
  the 
  amorphous 
  iodide 
  would 
  appear 
  to 
  be 
  5*8167. 
  

   This 
  applies 
  to 
  the 
  precipitated 
  iodide 
  which 
  had 
  been 
  several 
  times 
  fused, 
  

   and 
  with 
  which 
  the 
  principal 
  experiments 
  herein 
  described 
  were 
  made. 
  

   A 
  specimen 
  of 
  iodide 
  produced 
  by 
  the 
  direct 
  solution 
  of 
  silver 
  in 
  hydriodic 
  

   acid 
  gave 
  a 
  specific 
  gravity 
  of 
  5*812, 
  and 
  appeared 
  to 
  be 
  less 
  crystalline 
  

  

  * 
  " 
  Sur 
  les 
  proprieties 
  de 
  l'iodure 
  d'argent," 
  Comptes 
  Eendus, 
  vol. 
  Lriv. 
  

  

  