﻿414 
  MESSES. 
  A. 
  J. 
  JUKES-BROWNE 
  AND 
  W. 
  HILL 
  ON 
  COLLOID 
  

  

  [Since 
  this 
  paper 
  was 
  written, 
  one 
  of 
  us 
  has 
  had 
  the 
  opportunity 
  

   of 
  conferring 
  with 
  Mr. 
  J. 
  B. 
  Harrison, 
  formerly 
  of 
  Christ's 
  College, 
  

   Cambridge, 
  and 
  now 
  Island 
  Professor 
  of 
  Chemistry 
  in 
  Barbadoes. 
  

   He 
  kindly 
  offered 
  to 
  separate 
  the 
  several 
  kinds 
  of 
  siliceous 
  matter 
  

   for 
  us 
  by 
  elutriation 
  and 
  solution 
  in 
  caustic 
  potash, 
  and 
  a 
  sample 
  of 
  

   the 
  same 
  bed 
  was 
  analyzed 
  by 
  him 
  with 
  the 
  following 
  results 
  : 
  — 
  

  

  Moisture 
  1-08 
  

  

  Combined 
  water 
  and 
  traces 
  of 
  organic 
  

  

  matter 
  3*18 
  

  

  Colloid 
  silica 
  19-08 
  

  

  Quartz 
  and 
  a 
  little 
  mica 
  11-23 
  

  

  Clay 
  and 
  glauconite 
  *47 
  

  

  Carbonate 
  of 
  lime 
  and 
  magnesia 
  by 
  

  

  difference 
  64*96 
  

  

  100-00 
  

  

  Prof. 
  Harrison, 
  therefore, 
  makes 
  the 
  proportion 
  of 
  soluble 
  silica 
  

   rather 
  higher, 
  amounting 
  to 
  about 
  19 
  per 
  cent, 
  as 
  compared 
  with 
  

   the 
  15*4 
  per 
  cent, 
  of 
  the 
  first 
  analysis. 
  It 
  is 
  possible, 
  and 
  

   even 
  probable, 
  that 
  the 
  proportion 
  of 
  organic 
  silica 
  varies 
  consider- 
  

   ably 
  in 
  different 
  parts 
  of 
  the 
  rock, 
  and 
  that 
  to 
  obtain 
  an 
  accurate 
  

   estimate 
  of 
  the 
  average 
  amount, 
  several 
  samples 
  should 
  be 
  pounded 
  

   up 
  and 
  a 
  small 
  quantity 
  of 
  the 
  powder 
  so 
  obtained 
  submitted 
  to 
  

   analysis. 
  

  

  The 
  method 
  employed 
  by 
  Prof. 
  Harrison 
  in 
  estimating 
  the 
  amounts 
  

   of 
  the 
  several 
  siliceous 
  matters 
  was 
  as 
  follows 
  : 
  — 
  The 
  sample 
  was 
  

   ground 
  fine, 
  and 
  two 
  portions 
  of 
  about 
  2 
  or 
  3 
  grams 
  each 
  were 
  taken 
  

   and 
  dissolved 
  in 
  dilute 
  acetic 
  acid. 
  One 
  of 
  these 
  was 
  evaporated 
  to 
  

   dryness, 
  washed, 
  and 
  the 
  residue 
  weighed, 
  which 
  consists 
  of 
  the 
  

   total 
  iron, 
  alumina, 
  f 
  clay, 
  silica, 
  &c. 
  ; 
  call 
  this 
  residue 
  A 
  : 
  after 
  igni- 
  

   tion 
  it 
  is 
  heated 
  with 
  concentrated 
  sulphuric 
  acid 
  until 
  decomposed, 
  

   the 
  residue 
  boiled 
  with 
  dilute 
  hydrochloric 
  acid 
  to 
  remove 
  iron 
  and 
  

   alumina, 
  then 
  with 
  a 
  mixture 
  of 
  caustic 
  soda 
  and 
  carbonate 
  of 
  soda 
  

   solution, 
  which 
  dissolves 
  all 
  amorphous 
  silica 
  and 
  leaves 
  the 
  residue 
  

   of 
  mica 
  and 
  quartz-sand. 
  The 
  other 
  portion 
  is 
  not 
  evaporated, 
  but 
  

   washed 
  free 
  from 
  lime- 
  salts 
  and 
  then 
  washed 
  by 
  suction 
  with 
  a 
  hot 
  

   solution 
  of 
  mixed 
  caustic 
  soda 
  and 
  carbonate 
  of 
  soda, 
  washed 
  until 
  

   free 
  from 
  alkali, 
  and 
  weighed 
  ; 
  this 
  (B) 
  gives 
  the 
  clay, 
  glauconite, 
  

   and 
  insoluble 
  silica. 
  The 
  difference 
  between 
  A 
  and 
  B 
  gives 
  the 
  

   soluble 
  silica.] 
  

  

  It 
  only 
  remained 
  to 
  test 
  the 
  Eastcott 
  chalk 
  in 
  which 
  the 
  peculiar 
  

   cherty 
  nodules 
  were 
  found 
  and 
  to 
  see 
  if 
  that 
  material 
  gave 
  similar 
  

   results. 
  A 
  sample 
  of 
  this 
  was 
  sent 
  to 
  Mr. 
  J. 
  Brierley, 
  the 
  Borough 
  

   Analyst 
  of 
  Southampton, 
  who 
  had 
  very 
  kindly 
  offered 
  to 
  estimate 
  

   the 
  proportion 
  of 
  soluble 
  silica 
  for 
  us 
  ; 
  and 
  we 
  quote 
  the 
  following 
  

   from 
  his 
  report 
  : 
  — 
  

  

  " 
  The 
  total 
  insoluble 
  matter, 
  after 
  evaporating 
  the 
  hydrochloric- 
  

   acid 
  solution, 
  was 
  35-17 
  per 
  cent. 
  ; 
  of 
  this 
  there 
  was 
  

  

  