﻿602 
  Gooclt, 
  etc. 
  — 
  Dehydration 
  and 
  Recovery 
  of 
  Silica. 
  

  

  ing 
  to 
  a 
  constant 
  weight 
  the 
  silica 
  precipitated 
  in 
  the 
  ordinary 
  

   way, 
  by 
  the 
  action 
  of 
  acid 
  upon 
  the 
  products 
  of 
  fusion 
  with 
  an 
  

   alkali 
  carbonate, 
  is 
  not 
  due 
  to 
  the 
  obstinate 
  retention 
  of 
  water 
  

   but 
  to 
  the 
  presence 
  of 
  foreign 
  material 
  difficultly 
  volatile 
  or 
  

   slowly 
  changeable 
  at 
  the 
  temperature 
  of 
  ignition. 
  In 
  our 
  ex- 
  

   periments, 
  the 
  foreign 
  material 
  retained 
  in 
  the 
  precipitated 
  

   silica 
  must 
  have 
  been 
  sodium 
  chloride, 
  and 
  this 
  in 
  the 
  process 
  

   of 
  ignition 
  of 
  hydrous 
  silica 
  is, 
  as 
  we 
  have 
  found 
  experimen- 
  

   tally, 
  converted 
  by 
  the 
  action 
  of 
  water 
  to 
  sodium 
  oxide, 
  which 
  

   combines 
  with 
  the 
  silica. 
  In 
  the 
  experiments 
  described 
  above, 
  

   the 
  sodium 
  oxide 
  retained 
  by 
  0*5 
  grm. 
  of 
  silica 
  amounted 
  in 
  

   the 
  average 
  to 
  0*0005 
  grm. 
  After 
  the 
  treatment 
  with 
  sulphuric 
  

   acid 
  and 
  hydrofluoric 
  acid, 
  the 
  residue 
  ignited 
  at 
  red 
  heat 
  is 
  

   sodium 
  sulphate, 
  and 
  from 
  the 
  weight 
  found 
  of 
  this 
  substance 
  

   the 
  equivalent 
  weight 
  of 
  sodium 
  oxide 
  must 
  be 
  calculated 
  in 
  

   order 
  that 
  it 
  may 
  be 
  used 
  as 
  the 
  correction 
  for 
  the 
  foreign 
  

   material 
  included 
  in 
  the 
  silica 
  as 
  weighed. 
  In 
  the 
  final 
  igni- 
  

   tion 
  the 
  use 
  of 
  the 
  high 
  heat 
  of 
  the 
  blast 
  lamp 
  is 
  not 
  advisable, 
  

   lest 
  the 
  sodium 
  sulphate 
  lose 
  weight 
  and 
  so 
  vitiate 
  the 
  correc- 
  

   tion 
  to 
  be 
  applied 
  to 
  the 
  silica. 
  

  

  The 
  Recovery 
  of 
  Silica 
  after 
  Fusion 
  with 
  Sodium 
  Carbonate. 
  

  

  It 
  is 
  a 
  generally 
  recognized 
  fact* 
  that, 
  after 
  fusion 
  with 
  

   sodium 
  carbonate, 
  silica 
  cannot 
  be 
  recovered 
  completely 
  by 
  a 
  

   single 
  filtration 
  following 
  any 
  number 
  of 
  evaporations 
  and 
  

   treatments 
  with 
  hydrochloric 
  acid. 
  To 
  secure 
  satisfactory 
  

   results 
  it 
  is 
  necessary 
  to 
  evaporate 
  the 
  filtrate 
  after 
  the 
  removal 
  

   of 
  the 
  main 
  amount 
  of 
  silica 
  by 
  the 
  first 
  treatment, 
  treat 
  the 
  

   residue 
  with 
  hydrochloric 
  acid, 
  and 
  again 
  filter. 
  

  

  The 
  experiments 
  detailed 
  in 
  the 
  following 
  table 
  record 
  the 
  

   results 
  obtained 
  in 
  recovering 
  silica 
  by 
  two 
  such" 
  treatments 
  

   after 
  fusion 
  with 
  3 
  grm. 
  of 
  sodium 
  carbonate. 
  The 
  fused 
  mass 
  

   was 
  treated 
  with 
  hydrochloric 
  acid 
  ; 
  the 
  liquid 
  was 
  evaporated 
  

   on 
  the 
  steam 
  bath; 
  the 
  residue, 
  desiccated 
  either 
  at 
  110° 
  in 
  the 
  

   air 
  bath 
  or 
  by 
  the 
  treatment 
  with 
  acetic 
  anhydride; 
  according 
  

   to 
  the 
  method 
  and 
  for 
  the 
  purpose, 
  previously 
  described,! 
  was 
  

   extracted 
  with 
  hydrochloric 
  acid 
  ; 
  the 
  insoluble 
  silica 
  was 
  fil- 
  

   tered 
  off, 
  washed, 
  ignited, 
  and 
  weighed 
  ; 
  the 
  filtrate 
  from 
  the 
  

   silica 
  insoluble 
  in 
  this 
  first 
  operation 
  was 
  evaporated 
  ; 
  and 
  the 
  

   residue 
  obtained 
  was 
  treated 
  like 
  the 
  first 
  residue. 
  

  

  In 
  these 
  experiments 
  the 
  deficiency 
  in 
  silica 
  found 
  after 
  the 
  

   first 
  thorough 
  evaporation 
  and 
  desiccation 
  at 
  110° 
  amounts 
  in 
  

   the 
  average 
  to 
  0'0051 
  grm., 
  after 
  correcting 
  for 
  silica 
  intro- 
  

   duced 
  in 
  the 
  sodium 
  carbonate, 
  and 
  this 
  is 
  practically 
  the 
  

  

  * 
  Hillebrand, 
  Am. 
  Chem. 
  Jour., 
  xxiv, 
  366 
  : 
  Treadwell, 
  loc. 
  cit. 
  

   f 
  See 
  p. 
  599. 
  

  

  