﻿1874.] 
  

  

  Effects 
  of 
  Heat 
  on 
  Iodide 
  of 
  Silver. 
  

  

  103 
  

  

  of 
  the 
  iodide. 
  This 
  would 
  give 
  as 
  the 
  specific 
  gravity 
  of 
  the 
  molten 
  

   iodide 
  5-406. 
  The 
  mass 
  was 
  then 
  allowed 
  to 
  solidify 
  in 
  the 
  tube, 
  and 
  a 
  

   large 
  conical 
  cavity 
  appeared 
  at 
  the 
  moment 
  of 
  congelation. 
  This 
  cavity 
  

   contained 
  4*552 
  grammes 
  of 
  mercury, 
  and 
  would 
  contain 
  1*8149 
  gramme 
  

   of 
  iodide. 
  Hence, 
  if 
  the 
  volume 
  of 
  the 
  iodide 
  before 
  fusion 
  be 
  taken 
  as 
  

   100, 
  the 
  volume 
  of 
  the 
  resulting 
  fused 
  iodide 
  will 
  be 
  104*499. 
  Or, 
  

   again, 
  100 
  volumes 
  of 
  molten 
  iodide 
  contract 
  to 
  95*694 
  volumes 
  of 
  the 
  solid. 
  

   The 
  principal 
  expansion 
  takes 
  place 
  at 
  the 
  moment 
  of 
  fusion, 
  and 
  the 
  ex- 
  

   pansion 
  between 
  116° 
  C. 
  and 
  450° 
  C. 
  is 
  not 
  considerable. 
  No 
  really 
  satis- 
  

   factory 
  method 
  has 
  been 
  yet 
  found 
  for 
  determining 
  the 
  coefficient 
  of 
  

   expansion 
  between 
  116° 
  C. 
  and 
  450° 
  C. 
  ; 
  but 
  if 
  we 
  assume 
  it 
  to 
  be 
  equal 
  

   to 
  the 
  mean 
  expansion 
  on 
  the 
  other 
  side 
  of 
  116° 
  C. 
  (of 
  course 
  omitting 
  

   the 
  sudden 
  expansion 
  which 
  takes 
  place 
  when 
  the 
  amorphous 
  passes 
  into 
  

   the 
  crystalline 
  condition), 
  we 
  find 
  that 
  a 
  volume 
  1*00000 
  at 
  116° 
  C. 
  

   will 
  become 
  a 
  volume 
  of 
  1*01455238 
  at 
  450° 
  C. 
  just 
  below 
  the 
  melting- 
  

   point, 
  while 
  in 
  passing 
  from 
  the 
  solid 
  to 
  the 
  liquid 
  condition 
  the 
  volume 
  

   increases 
  from 
  1*01455 
  to 
  1*04499, 
  an 
  expansion 
  ='03044. 
  

  

  When 
  a 
  mass 
  of 
  iodide 
  of 
  silver 
  passes 
  from 
  the 
  amorphous 
  into 
  the 
  

   crystalline 
  condition 
  the 
  molecular 
  commotion 
  is 
  so 
  considerable 
  that 
  

   portions 
  of 
  the 
  mass 
  are 
  sometimes 
  jerked 
  off 
  from 
  the 
  ends 
  of 
  a 
  bar, 
  and 
  

   large 
  fissures 
  appear 
  in 
  the 
  mass. 
  These 
  are 
  sometimes 
  as 
  much 
  as 
  half 
  

   a 
  millimetre 
  broad 
  and 
  several 
  centimetres 
  long 
  in 
  a 
  cylindrical 
  mass 
  

   weighing 
  from 
  10 
  to 
  20 
  grammes. 
  They 
  penetrate 
  to 
  the 
  centre 
  of 
  the 
  

   mass, 
  as 
  may 
  be 
  shown 
  by 
  cooling 
  the 
  iodide 
  under 
  mercury, 
  when 
  the 
  

   whole 
  mass 
  is 
  found 
  to 
  be 
  permeated 
  by 
  the 
  metal. 
  The 
  capacity 
  of 
  these 
  

   intercrystalline 
  spaces 
  was 
  determined 
  by 
  allowing 
  a 
  known 
  weight 
  of 
  

   iodide 
  to 
  pass 
  from 
  its 
  amorphous 
  to 
  its 
  crystalline 
  condition 
  beneath 
  the 
  

   surface 
  of 
  mercury, 
  and 
  again 
  weighing. 
  

  

  «. 
  3*643 
  grammes 
  Agl 
  after 
  thus 
  cooling 
  weighed 
  3*968 
  grammes. 
  

  

  ,<3. 
  5*913 
  „ 
  „ 
  „ 
  „ 
  6*417 
  

  

  And 
  as 
  we 
  know 
  the 
  specific 
  gravity 
  of 
  mercury 
  and 
  of 
  the 
  iodide, 
  it 
  is 
  

   easy 
  to 
  deduce 
  from 
  the 
  above 
  that 
  the 
  volume 
  of 
  the 
  cracks 
  is 
  repre- 
  

   sented 
  respectively 
  by 
  (a) 
  -1353 
  gramme 
  and 
  (/3) 
  *2098 
  gramme 
  of 
  

   iodide; 
  hence 
  

  

  a. 
  3*643 
  : 
  *1353 
  : 
  : 
  100 
  : 
  3*7112 
  

   (d. 
  5*913 
  : 
  -2098 
  : 
  : 
  100 
  : 
  3*5481 
  

  

  which 
  give 
  a 
  mean 
  of 
  3*6296. 
  Therefore 
  100 
  grammes 
  of 
  iodide 
  in 
  the 
  

   amorphous 
  condition 
  produce, 
  in 
  passing 
  into 
  the 
  crystalline 
  condition, 
  

   intercrystalline 
  spaces 
  capable 
  of 
  containing 
  3*6296 
  grammes 
  of 
  iodide. 
  

   From 
  an 
  observation 
  which 
  was 
  made 
  on 
  a 
  cylindrical 
  mass 
  of 
  iodide 
  a 
  

   centimetre 
  diameter, 
  which 
  in 
  undergoing 
  expansion 
  in 
  the 
  passage 
  from 
  

   the 
  amorphous 
  to 
  the 
  crystalline 
  condition 
  had 
  produced 
  a 
  separation 
  

   amounting 
  to 
  half 
  a 
  millimetre 
  in 
  a 
  tube 
  which 
  had 
  yielded 
  to 
  the 
  expan- 
  

   sion, 
  the 
  expansion 
  of 
  the 
  mass, 
  plus 
  the 
  intercrystalline 
  spaces 
  within 
  

  

  