﻿338 
  Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  no 
  satisfactory 
  answer 
  can 
  as 
  yet 
  be 
  given, 
  the 
  discussion 
  

   and 
  recording 
  of 
  some 
  observations 
  in 
  this 
  connection 
  

   may 
  be 
  useful 
  in 
  calling 
  attention 
  to 
  the 
  problems 
  

   involved. 
  

  

  No 
  thermal 
  or 
  optical 
  indications 
  of 
  a 
  transformation 
  

   of 
  either 
  lepidocrocite 
  or 
  goethite 
  could 
  be 
  observed 
  on 
  

   heating 
  them 
  between 
  room 
  temperature 
  and 
  the 
  temper- 
  

   ature 
  at 
  which 
  they 
  decompose. 
  -The 
  transformation 
  

   may 
  take 
  place 
  at 
  a 
  different 
  temperature 
  or 
  be 
  very 
  slow 
  

   and 
  it 
  is 
  not 
  certain 
  whether 
  their 
  relation 
  is 
  enantiotro- 
  

   pic 
  or 
  monotropic. 
  The 
  microscopic 
  study 
  of 
  some 
  of 
  

   our 
  specimens 
  (see 
  p. 
  346) 
  revealed 
  that 
  it 
  is 
  not 
  uncom- 
  

   mon 
  to 
  find 
  lepidocrocite 
  and 
  goethite 
  together, 
  with 
  

   either 
  as 
  the 
  earlier 
  mineral. 
  It 
  would 
  seem 
  that 
  the 
  

   conditions 
  of 
  their 
  formation 
  could 
  not 
  have 
  been 
  very 
  

   different. 
  However, 
  as 
  no 
  crystals 
  of 
  goethite 
  and 
  lepi- 
  

   docrocite 
  have 
  so 
  far 
  been 
  artificially 
  prepared 
  and 
  their 
  

   solubilities 
  are 
  not 
  known, 
  there 
  is 
  nothing 
  to 
  indicate 
  

   their 
  stability 
  relation. 
  It 
  is 
  probable 
  that 
  field 
  observa- 
  

   tions 
  will 
  aid 
  materially 
  in 
  the 
  solution 
  of 
  this 
  problem. 
  

  

  Not 
  only 
  are 
  goethite 
  and 
  lepidocrocite 
  found 
  together, 
  

   but 
  turgite 
  (the 
  solid 
  solution) 
  may 
  similarly 
  appear 
  with 
  

   either 
  of 
  them. 
  Pelikan 
  45 
  observed 
  on 
  some 
  Brazilian 
  

   specimens 
  the 
  formation 
  of 
  turgite 
  on 
  fibrous 
  goethite 
  46 
  

   and 
  from 
  microscopic 
  observations 
  of 
  their 
  structure 
  he 
  

   concluded 
  that 
  the 
  turgite 
  could 
  not 
  have 
  been 
  derived 
  by 
  

   the 
  dehydration 
  of 
  the 
  goethite, 
  but 
  must 
  have 
  been 
  

   deposited 
  there 
  directly. 
  

  

  Our 
  observations 
  (see 
  description 
  of 
  specimens 
  — 
  lepi- 
  

   docrocite, 
  Siegen, 
  and 
  R. 
  C. 
  1489) 
  lead 
  us 
  to 
  the 
  same 
  

   conclusion, 
  i. 
  e., 
  that 
  turgite 
  is 
  not 
  necessarily 
  a 
  dehydra- 
  

   tion 
  product 
  of 
  goethite 
  or 
  lepidocrocite. 
  

  

  Red 
  and 
  yellow 
  ferric 
  oxides 
  often 
  occur 
  in 
  nature 
  

   together, 
  and 
  the 
  assumption 
  is 
  frequently 
  advanced 
  that 
  

   the 
  red 
  ferric 
  oxides 
  are 
  derived 
  from 
  the 
  yellow 
  ones. 
  

   It 
  has 
  been 
  supposed 
  that 
  in 
  nature 
  gradual 
  dehydration 
  

   of 
  higher 
  hydrates 
  to 
  some 
  more 
  stable 
  ones 
  or 
  to 
  anhy- 
  

   drous 
  ferric 
  oxide 
  takes 
  place 
  under 
  the 
  influence 
  of 
  salt 
  

   solutions 
  or 
  by 
  atmospheric 
  weathering. 
  47 
  This 
  theory 
  

   appeared 
  plausible 
  as 
  long 
  as 
  a 
  series 
  of 
  hydrates 
  was 
  

   supposed 
  to 
  exist, 
  as 
  it 
  is 
  obviously 
  impossible 
  for 
  several 
  

  

  ■ 
  Tseh. 
  Mitth., 
  14, 
  1. 
  

   ** 
  Pelikan 
  describes 
  it 
  as 
  limonite. 
  

  

  47 
  Rtremme, 
  Zs. 
  prakt, 
  Geol. 
  18, 
  18, 
  1910; 
  Cornu, 
  Zs. 
  Chem. 
  und 
  Ind. 
  d. 
  

   Kolloide, 
  4, 
  285, 
  1909. 
  

  

  