﻿Posnjdk 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  333 
  

  

  As 
  seen 
  from 
  Table 
  V 
  this 
  ratio 
  in 
  all 
  cases 
  is 
  practi- 
  

   cally 
  one. 
  The 
  fact 
  that 
  in 
  most 
  cases 
  a 
  slightly 
  smaller 
  

   value 
  was 
  obtained 
  is 
  probably 
  caused 
  by 
  adsorption, 
  due 
  

   to 
  the 
  increase 
  in 
  surface 
  on 
  decomposition. 
  

  

  Slow 
  dehydration 
  of 
  turgite 
  confirmed 
  the 
  earlier 
  con- 
  

   clusion, 
  derived 
  from 
  the 
  rapid 
  curves, 
  that 
  this 
  sub- 
  

   stance 
  differs 
  essentially 
  from 
  the 
  other 
  hydrated 
  ferric 
  

   oxides. 
  The 
  curves 
  are 
  given 
  in 
  fig. 
  3 
  (No. 
  4 
  and 
  3). 
  

   They 
  are 
  smooth 
  and 
  show 
  that 
  water 
  is 
  given 
  off 
  grad- 
  

   ually 
  with 
  every 
  increase 
  in 
  temperature. 
  No 
  sudden 
  

   decomposition 
  takes 
  place 
  anywhere 
  and 
  it 
  would 
  seem 
  

   that 
  turgite, 
  unlike 
  the 
  other 
  hydrated 
  ferric 
  oxides, 
  is 
  

   not 
  a 
  definitely 
  hydrated 
  compound. 
  The 
  water 
  this 
  sub- 
  

   stance 
  contains 
  must 
  either 
  be 
  adsorbed 
  or 
  in 
  solid 
  solu- 
  

   tion, 
  or 
  both. 
  Some 
  indication 
  as 
  to 
  the 
  way 
  in 
  which 
  the 
  

   water 
  is 
  held 
  may 
  be 
  found 
  in 
  a 
  rehydration 
  experiment. 
  

   But 
  little 
  water 
  was 
  taken 
  up 
  by 
  the 
  dehydrated 
  substance 
  

   on 
  standing 
  in 
  the 
  room 
  for 
  over 
  two 
  weeks, 
  and 
  on 
  the 
  

   subsequent 
  dehydration 
  up 
  to 
  the 
  highest 
  temperature 
  it 
  

   had 
  the 
  same 
  composition 
  as 
  formerly. 
  This 
  could 
  not 
  

   very 
  well 
  be 
  the 
  behavior 
  of 
  adsorbed 
  water, 
  for 
  reversi- 
  

   bility 
  in 
  water 
  content 
  is 
  characteristic 
  in 
  such 
  cases 
  pro- 
  

   vided 
  no 
  change 
  of 
  gross 
  structure 
  takes 
  place 
  (seep. 
  331). 
  

   It 
  appears, 
  therefore, 
  more 
  likely 
  that 
  the 
  water 
  in 
  tur- 
  

   gite 
  is 
  largely 
  held 
  in 
  solid 
  solution. 
  Support 
  of 
  this 
  

   view 
  was 
  found 
  later 
  in 
  some 
  other 
  observations 
  (see 
  den- 
  

   sity 
  and 
  microscopical 
  descriptions). 
  41 
  

  

  Considering 
  the 
  evidence 
  presented 
  by 
  the 
  dehydration 
  

   experiments, 
  we 
  come 
  to 
  the 
  conclusion 
  that 
  no 
  series 
  of 
  

   hydrates 
  of 
  ferric 
  oxide 
  exists. 
  According 
  to 
  the 
  evi- 
  

   dence 
  presented 
  the 
  only 
  definite 
  compound 
  actually 
  in 
  

   existence 
  is 
  ferric 
  oxide 
  monohydrate. 
  Goethite 
  has 
  long 
  

   been 
  recognized 
  as 
  such 
  a 
  compound 
  and 
  the 
  present 
  

   study 
  definitely 
  established 
  lepidocrocite 
  as 
  another 
  sub- 
  

   stance 
  of 
  the 
  same 
  composition. 
  As 
  previously 
  men- 
  

   tioned, 
  Hintze 
  42 
  concluded 
  on 
  the 
  basis 
  of 
  Fischer 
  's 
  work 
  

   that 
  "limonite" 
  is 
  the 
  "colloidal 
  form 
  of 
  goethite. 
  " 
  In 
  

   view 
  of 
  the 
  facts 
  brought 
  forward 
  in 
  the 
  present 
  paper 
  

   such 
  a 
  conclusion 
  seems 
  rather 
  hasty 
  and, 
  using 
  the 
  same 
  

   terminology, 
  it 
  seems 
  that 
  "limonite" 
  could 
  just 
  as 
  well 
  

   be 
  the 
  colloidal 
  form 
  of 
  lepidocrocite. 
  However, 
  as 
  the 
  

   term 
  colloidal 
  does 
  not 
  imply 
  anything 
  about 
  the 
  modifi- 
  

   cation 
  of 
  the 
  substance 
  (it 
  can 
  properly 
  be 
  used 
  only 
  to 
  

  

  41 
  Support 
  of 
  this 
  view 
  may 
  also 
  be 
  found 
  in 
  the 
  dehydration 
  of 
  the 
  

   specimen 
  from 
  Germany 
  (Table 
  I, 
  No. 
  1). 
  This 
  substance 
  contained 
  1-3% 
  

   water 
  but 
  lost 
  less 
  than 
  0-2% 
  on 
  heating 
  to 
  300°. 
  

  

  ^Handbuch 
  der 
  Mineralogie, 
  I 
  (2), 
  p. 
  2008. 
  

  

  