﻿106 
  Mr. 
  G. 
  F. 
  Rodwell 
  on 
  the 
  [Dec. 
  10, 
  

  

  the 
  expansion 
  of 
  the 
  glass, 
  agree 
  very 
  well 
  with 
  Kegnault's 
  determina- 
  

   tions 
  of 
  the 
  absolute 
  expansion 
  of 
  mercury. 
  Then 
  38*3680 
  grammes 
  of 
  

   the 
  fused 
  iodide 
  were 
  placed 
  in 
  the 
  flask 
  ; 
  it 
  was 
  filled 
  up 
  with 
  mercury, 
  

   the 
  whole 
  was 
  heated, 
  cooled 
  in 
  a 
  good 
  vacuum, 
  weighed, 
  cooled 
  to 
  

   —18° 
  C. 
  (— 
  0°*4 
  F.) 
  and 
  weighed. 
  The 
  flask 
  was 
  then 
  heated 
  respec- 
  

   tively 
  to 
  0° 
  C, 
  21° 
  C, 
  67° 
  C, 
  and 
  the 
  weights 
  determined. 
  At 
  high 
  

   temperatures 
  the 
  mercury 
  acts 
  upon 
  the 
  iodide 
  and 
  a 
  green 
  iodide 
  of 
  

   mercury 
  is 
  formed. 
  The 
  results 
  were 
  not 
  very 
  concordant 
  above 
  67° 
  C. 
  

   and 
  have 
  not 
  been 
  introduced. 
  The 
  general 
  results 
  were 
  as 
  follows 
  : 
  

   the 
  amounts 
  of 
  mercury 
  driven 
  from 
  the 
  flask 
  for 
  1° 
  C. 
  were 
  re- 
  

   spectively 
  — 
  

  

  Between 
  

  

  -18° 
  

  

  and 
  0° 
  

  

  C. 
  = 
  

  

  •052648 
  

  

  -18° 
  

  

  „ 
  +21° 
  

  

  C. 
  = 
  

  

  •051392 
  

  

  0° 
  

  

  „ 
  +21° 
  

  

  c. 
  = 
  

  

  •050285 
  

  

  -18° 
  

  

  » 
  +67° 
  

  

  c. 
  = 
  

  

  •049684 
  

  

  0° 
  

  

  „ 
  67° 
  

  

  c. 
  = 
  

  

  •048873 
  

  

  + 
  21° 
  

  

  a 
  67° 
  

  

  c. 
  = 
  

  

  •048228 
  

  

  Now 
  from 
  the 
  known 
  weight 
  of 
  mercury 
  in 
  the 
  flask 
  and 
  the 
  known 
  

   expansion 
  of 
  mercury, 
  it 
  is 
  easy 
  to 
  deduce 
  the 
  quantity 
  of 
  mercury 
  which 
  

   ought 
  to 
  have 
  been 
  driven 
  from 
  the 
  flask 
  by 
  expansion 
  for 
  any 
  number 
  

   of 
  degrees 
  ; 
  and 
  having 
  determined 
  the 
  actual 
  amount 
  of 
  mercury 
  ex- 
  

   pelled, 
  we 
  at 
  once 
  find 
  the 
  contraction 
  of 
  the 
  known 
  weight 
  of 
  iodide 
  of 
  

   silver 
  from 
  known 
  number 
  of 
  degrees 
  by 
  subtracting 
  the 
  amount 
  of 
  

   mercury 
  expelled 
  from 
  the 
  amount 
  of 
  mercury 
  which 
  ought 
  to 
  have 
  

   been 
  expelled 
  if 
  the 
  iodide 
  had 
  not 
  been 
  present. 
  We 
  can 
  thus 
  arrive 
  at 
  

   the 
  coefficient 
  of 
  contraction 
  of 
  the 
  iodide 
  for 
  one 
  degree 
  Centigrade. 
  

   This 
  appears 
  to 
  be 
  -00000718 
  for 
  temperatures 
  between 
  —18° 
  C. 
  and 
  

   0° 
  C, 
  -00003297 
  for 
  temperatures 
  between 
  0° 
  C. 
  and 
  21° 
  C, 
  and 
  

   •00005570 
  for 
  temperatures 
  between 
  21° 
  and 
  67° 
  C. 
  Thus 
  the 
  coefficient 
  

   augments 
  with 
  the 
  temperature. 
  The 
  following 
  Table 
  (p. 
  107) 
  represents 
  

   the 
  relationship 
  between 
  the 
  effects 
  of 
  heat 
  on 
  iodide 
  of 
  silver 
  and 
  on 
  mer- 
  

   cury. 
  It 
  cannot 
  be 
  regarded 
  as 
  more 
  than 
  an 
  approximation 
  until 
  more 
  

   perfect 
  methods 
  for 
  investigating 
  the 
  actions 
  can 
  be 
  devised. 
  The 
  ex- 
  

   treme 
  peculiarities 
  of 
  the 
  molecular 
  constitution 
  of 
  the 
  iodide, 
  com- 
  

   bined 
  with 
  the 
  fact 
  that 
  it 
  cannot 
  be 
  raised 
  to 
  a 
  high 
  temperature 
  

   in 
  mercury 
  without 
  suffering 
  decomposition, 
  and 
  that 
  its 
  fusing- 
  

   point 
  is 
  above 
  the 
  boiling-point 
  of 
  mercury, 
  render 
  experiments 
  of 
  

   this 
  nature, 
  especially 
  when 
  a 
  high 
  temperature 
  is 
  required, 
  unsatis- 
  

   factory. 
  

  

  