﻿Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  315 
  

  

  with 
  the 
  substance 
  of 
  the 
  composition 
  2Fe 
  2 
  3 
  -3 
  H 
  2 
  pre- 
  

   pared 
  under 
  pressure 
  by 
  Ruff, 
  12 
  which 
  however 
  he 
  thinks 
  

   is 
  unstable 
  and 
  therefore 
  does 
  not 
  occur 
  as 
  a 
  mineral. 
  

   Among 
  the 
  minerals 
  he 
  doubts 
  the 
  existence 
  of 
  xantho- 
  

   siderite 
  and 
  believes 
  turgite 
  to 
  be 
  a 
  dehydrated 
  limonite. 
  

  

  As 
  seen 
  from 
  this 
  short 
  review 
  little 
  definite 
  knowledge 
  

   exists 
  in 
  respect 
  to 
  any 
  of 
  the 
  hydrated 
  ferric 
  oxides, 
  

   except 
  goethite, 
  and 
  many 
  contradictory 
  conclusions 
  have 
  

   been 
  drawn. 
  Chemically 
  as 
  well 
  as 
  mineralogically 
  the 
  

   problem 
  presents 
  many 
  difficulties 
  and 
  up 
  to 
  the 
  present 
  

   apparently 
  no 
  systematic 
  investigation 
  had 
  been 
  under- 
  

   taken 
  involving 
  the 
  correlation 
  of 
  different 
  properties. 
  

   In 
  view 
  of 
  the 
  abundance 
  of 
  hydrated 
  ferric 
  oxides 
  in 
  

   nature 
  and 
  the 
  widespread 
  interest 
  in 
  the 
  processes 
  of 
  

   formation 
  of 
  ore 
  bodies, 
  more 
  definite 
  information 
  about 
  

   the 
  nature 
  and 
  properties 
  of 
  the 
  hydrated 
  ferric 
  oxides 
  

   was 
  thought 
  desirable. 
  

  

  The 
  plan 
  of 
  this 
  investigation 
  was, 
  on 
  the 
  one 
  hand, 
  to 
  

   examine 
  chemically 
  and 
  microscopically 
  a 
  large 
  number 
  

   of 
  hydrated 
  iron 
  oxides 
  and 
  to 
  determine 
  their 
  physical 
  

   properties 
  ; 
  on 
  the 
  other, 
  to 
  synthesize 
  them, 
  if 
  possible, 
  

   by 
  the 
  study 
  of 
  a 
  chemical 
  system 
  in 
  which 
  they 
  were 
  

   likely 
  to 
  occur. 
  As 
  such 
  the 
  system 
  Fe 
  2 
  3 
  -S0 
  3 
  -H 
  2 
  was 
  

   chosen. 
  The 
  results 
  of 
  the 
  study 
  of 
  this 
  system 
  were, 
  

   however, 
  disappointing, 
  as 
  only 
  ' 
  ' 
  amorphous 
  ' 
  ' 
  and 
  no 
  

   crystallized 
  hydrated 
  ferric 
  oxide 
  was 
  formed. 
  Simi- 
  

   larly 
  various 
  single 
  experiments 
  aiming 
  at 
  the 
  formation 
  

   of 
  crystallized 
  hydrated 
  ferric 
  oxides 
  were 
  unsuccessful. 
  

   This 
  led 
  us 
  to 
  resort 
  to 
  thermal 
  methods 
  which, 
  combined 
  

   with 
  the 
  chemical 
  examinations 
  and 
  the 
  measured 
  physi- 
  

   cal 
  properties 
  of 
  the 
  hydrated 
  ferric 
  oxides, 
  yielded 
  some 
  

   of 
  the 
  desired 
  information. 
  

  

  Analyses. 
  

  

  A 
  large 
  number 
  of 
  analyses 
  of 
  hydrated 
  ferric 
  oxides 
  

   is 
  found 
  in 
  the 
  chemical 
  and 
  mineralogical 
  literatures. 
  

   However, 
  most 
  of 
  them, 
  except 
  those 
  of 
  crystallized 
  goe- 
  

   thite, 
  were 
  made 
  on 
  materials 
  not 
  sufficiently 
  defined 
  

   physically, 
  and 
  accordingly 
  show 
  unaccountable 
  varia- 
  

   tions 
  to 
  such 
  an 
  extent 
  that 
  from 
  them 
  no 
  definite 
  conclu- 
  

   sions 
  as 
  to 
  the 
  hydrated 
  form 
  which 
  they 
  represent 
  could 
  

   safely 
  be 
  drawn. 
  Most 
  analyses 
  are 
  also 
  comparatively 
  

   old 
  and 
  for 
  that 
  reason 
  probably 
  unsatisfactory 
  in 
  respect 
  

  

  12 
  Loc. 
  cit. 
  

  

  