﻿332 
  Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  and 
  third 
  branches 
  of 
  the 
  original 
  dehydration 
  curves. 
  

   Judging 
  from 
  the 
  smoothness 
  of 
  the 
  curves, 
  the 
  quick 
  

   adjustment, 
  and 
  the 
  reversibility 
  of 
  the 
  water 
  contents, 
  

   it 
  is 
  probable 
  that 
  it 
  is 
  due 
  largely 
  to 
  adsorption. 
  That 
  

   adsorption 
  of 
  moisture 
  to 
  a 
  considerable 
  extent 
  would 
  

   take 
  place 
  could 
  readily 
  be 
  foreseen 
  from 
  the 
  fibrous 
  

   (crystalline) 
  and 
  aggregated 
  structure 
  of 
  most 
  hydrated 
  

   ferric 
  oxides. 
  

  

  The 
  part 
  of 
  the 
  dehydration 
  curve 
  which 
  gives 
  infor- 
  

   mation 
  about 
  the 
  chemical 
  nature 
  of 
  the 
  substances 
  in 
  

   question, 
  and 
  is 
  therefore 
  of 
  greater 
  interest, 
  is 
  the 
  mid- 
  

   dle 
  portion. 
  It 
  is 
  formed 
  by 
  tjie 
  decomposition 
  of 
  the 
  

   substance, 
  and 
  the 
  amount 
  of 
  water 
  lost 
  in 
  this 
  portion 
  

   serves 
  for 
  the 
  chemical 
  identification 
  of 
  the 
  substance. 
  

   These 
  amounts 
  may 
  be 
  approximately 
  estimated 
  40 
  in 
  the 
  

   graphic 
  way 
  from 
  the 
  plots 
  of 
  the 
  dehydration 
  curves 
  as 
  

   follows 
  : 
  a 
  parallel 
  to 
  the 
  ordinate 
  is 
  drawn 
  from 
  the 
  

   point 
  at 
  which 
  decomposition 
  begins 
  and 
  the 
  lower 
  branch 
  

   of 
  the 
  dehydration 
  curve 
  is 
  continued 
  in 
  the 
  direction 
  

   indicated 
  by 
  its 
  curvature 
  to 
  the 
  intersection 
  with 
  that 
  

   line. 
  The 
  distance 
  between 
  the 
  upper 
  point 
  and 
  the 
  inter- 
  

   section 
  below 
  indicates 
  approximately 
  the 
  percentage 
  of 
  

   chemically 
  combined 
  water. 
  Comparison 
  on 
  a 
  mol 
  basis 
  

   of 
  this 
  amount 
  of 
  water 
  with 
  the 
  amount 
  of 
  ferric 
  oxide 
  

   determined 
  will 
  indicate 
  the 
  chemical 
  nature 
  of 
  the 
  com- 
  

   pound. 
  

  

  Table 
  V. 
  

  

  No. 
  of 
  analysis 
  Graphical 
  estimation 
  Mol. 
  ratio 
  

  

  in 
  Tables 
  of 
  % 
  of 
  combined 
  Fe 
  2 
  3 
  : 
  Name 
  of 
  miner- 
  

  

  I 
  and 
  III 
  % 
  Fe 
  2 
  3 
  H 
  2 
  H 
  2 
  al 
  as 
  received 
  

  

  5 
  89-65 
  9-1 
  1 
  : 
  0-90 
  Goethite 
  

  

  7 
  86-39 
  8-2 
  1:0-84 
  Xanthosiderite 
  

  

  8 
  88-24 
  9-0 
  1 
  : 
  091 
  Limonite 
  

  

  9 
  8719 
  9-4 
  1 
  : 
  0-96 
  Goethite 
  

  

  12 
  82-67 
  9-4 
  1 
  : 
  101 
  Lepidocrocite 
  

  

  13 
  8212 
  9-0 
  1:0-97 
  Limonite 
  

  

  14 
  83-47 
  8-8 
  1 
  : 
  0-94 
  Limonite 
  

  

  15 
  80-67 
  8-8 
  1 
  : 
  0-97 
  Limonite 
  

  

  17 
  81-15 
  8-9 
  1:0-97 
  Limonite 
  

  

  18 
  8013 
  8-2 
  1:0-91 
  Limonite 
  

  

  19 
  83-34 
  8-8 
  1 
  : 
  0-94 
  -."Amorphous" 
  

  

  22 
  7618 
  80 
  1 
  -0-93 
  LV^ated 
  fer- 
  

   „ 
  A 
  ^ 
  _ 
  ' 
  fric 
  oxides 
  

  

  23 
  74 
  ' 
  95 
  90 
  1 
  : 
  106 
  J 
  (gossan 
  ores) 
  

  

  40 
  These 
  estimates 
  may 
  not 
  represent 
  the 
  exact 
  amount 
  of 
  water 
  lost 
  by 
  the 
  

   substance 
  on 
  decomposition. 
  Decomposition 
  somewhat 
  changes 
  the 
  physical 
  

   structure 
  and 
  thus 
  through 
  ab- 
  or 
  adsorption 
  may 
  influence 
  the 
  position 
  of 
  

   the 
  lower 
  branch 
  of 
  the 
  curve. 
  However, 
  this 
  probably 
  would 
  not 
  cause 
  a 
  

   Utrge 
  enough 
  error 
  to 
  change 
  the 
  results. 
  

  

  