﻿1874.] 
  

  

  Effects 
  of 
  Heat 
  on 
  Iodide 
  of 
  Silver. 
  

  

  99 
  

  

  metallic 
  state, 
  and 
  forming 
  an 
  opaque 
  metallic 
  film 
  on 
  the 
  parts 
  of 
  the 
  

   surface 
  which 
  have 
  been 
  exposed 
  to 
  light." 
  

  

  The 
  following 
  experiments 
  were 
  made 
  to 
  determine 
  the 
  degree 
  of 
  sen- 
  

   sitiveness 
  of 
  the 
  iodide 
  to 
  light 
  : 
  — 
  

  

  a. 
  By 
  means 
  of 
  a 
  large 
  lens 
  the 
  rays 
  of 
  the 
  electric 
  lamp 
  were 
  brought 
  

   to 
  a 
  focus 
  within 
  a 
  glass 
  cell 
  containing 
  a 
  solution 
  of 
  iodide 
  of 
  potas- 
  

   sium 
  ; 
  a 
  solution 
  of 
  nitrate 
  of 
  silver 
  was 
  then 
  introduced 
  by 
  a 
  pipette 
  at 
  

   the 
  apex 
  of 
  the 
  cone 
  of 
  rays. 
  The 
  precipitated 
  iodide 
  possessed 
  its 
  

   usual 
  pale 
  yellow 
  colour. 
  

  

  /3. 
  Freshly 
  precipitated 
  iodide 
  in 
  suspension, 
  with 
  a 
  slight 
  excess 
  of 
  

   iodide 
  of 
  potassium, 
  remained 
  in 
  the 
  full 
  glare 
  of 
  a 
  July 
  sun 
  without 
  

   undergoing 
  any 
  perceptible 
  change 
  ; 
  neither 
  did 
  it 
  subsequently 
  darken. 
  

  

  y. 
  Freshly 
  precipitated 
  iodide 
  in 
  suspension, 
  with 
  a 
  slight 
  excess 
  of 
  

   nitrate 
  of 
  silver, 
  underwent 
  no 
  immediate 
  change 
  on 
  exposure 
  to 
  a 
  July 
  

   sun. 
  At 
  the 
  end 
  of 
  an 
  hour 
  it 
  had 
  become 
  slightly 
  grey, 
  and 
  subse- 
  

   quently 
  darkened. 
  

  

  Organic 
  matter 
  in 
  the 
  shape 
  of 
  starch-paste 
  did 
  not 
  induce 
  any 
  

   change 
  when 
  mixed 
  with 
  freshly 
  precipitated 
  iodide 
  in 
  suspension 
  with 
  

   a 
  slight 
  excess 
  of 
  iodide 
  of 
  potassium. 
  Albumenized 
  paper 
  with 
  iodide 
  

   precipitated 
  upon 
  it 
  did 
  not 
  undergo 
  any 
  immediate 
  change. 
  

  

  e. 
  Some 
  dried 
  and 
  powdered 
  iodide 
  was 
  found 
  to 
  have 
  acquired 
  a 
  

   slight 
  greyish 
  metallic 
  tinge 
  after 
  an 
  hour's 
  exposure 
  to 
  the 
  sun. 
  A 
  

   freshly 
  broken 
  surface 
  of 
  fused 
  iodide 
  became 
  very 
  slightly 
  darker 
  after 
  

   exposure 
  to 
  the 
  sun. 
  A 
  very 
  pale 
  microscopical 
  crystal 
  of 
  iodide, 
  re- 
  

   moved 
  from 
  the 
  interior 
  of 
  a 
  crystalline 
  mass, 
  became 
  slightly 
  brown 
  

   after 
  several 
  hours' 
  exposure 
  to 
  diffused 
  light. 
  

  

  £. 
  Crystals 
  of 
  iodide 
  of 
  silver 
  produced 
  by 
  direct 
  solution 
  of 
  silver 
  in 
  

   hydriodic 
  acid 
  were 
  not 
  affected 
  by 
  light 
  ; 
  neither 
  were 
  crystals 
  of 
  

   hydro-argentic 
  iodide 
  (AglHI), 
  nor 
  crystals 
  of 
  argento-potassic 
  iodide 
  

   (AglKI). 
  

  

  7]. 
  A 
  sheet 
  of 
  silver 
  leaf 
  was 
  exposed 
  to 
  the 
  vapour 
  of 
  iodine 
  (pro- 
  

   duced 
  by 
  spontaneous 
  evaporation) 
  for 
  five 
  minutes; 
  it 
  possessed 
  a 
  

   faintly 
  yellow 
  tinge, 
  which 
  on 
  exposure 
  to 
  the 
  sun 
  instantly 
  became 
  

   pale 
  green, 
  but 
  on 
  further 
  exposure 
  returned 
  to 
  its 
  original 
  pale 
  yellow. 
  

   A 
  second 
  sheet 
  was 
  exposed 
  for 
  ten 
  minutes 
  to 
  the 
  vapour 
  of 
  iodine 
  ; 
  it 
  

   acquired 
  a 
  golden-yellow 
  surface, 
  which 
  on 
  exposure 
  to 
  diffused 
  light 
  

   acquired 
  a 
  purplish-red 
  colour, 
  and 
  on 
  exposure 
  to 
  the 
  sun 
  became 
  

   greenish 
  purple. 
  On 
  continued 
  exposure 
  this 
  colour 
  disappeared, 
  and 
  

   the 
  plate 
  returned 
  to 
  almost 
  the 
  original 
  yellow 
  colour. 
  

  

  0. 
  A 
  sheet 
  of 
  silver 
  leaf 
  was 
  exposed 
  to 
  the 
  vapour 
  of 
  iodine 
  for 
  half 
  an 
  

   hour, 
  at 
  the 
  end 
  of 
  which 
  time 
  it 
  possessed 
  a 
  decided 
  golden 
  yellow 
  colour 
  ; 
  

   on 
  exposure 
  to 
  the 
  sun 
  it 
  instantly 
  acquired 
  a 
  dark 
  purple 
  colour, 
  edged 
  

   with 
  green 
  at 
  those 
  parts 
  least 
  exposed 
  to 
  the 
  direct 
  vapour 
  of 
  the 
  iodine. 
  

   On 
  continued 
  exposure 
  the 
  purple 
  became 
  paler, 
  but 
  the 
  sheet 
  did 
  not 
  

   return 
  to 
  its 
  original 
  yellow 
  colour. 
  

  

  