﻿THE 
  

  

  AMERICAN 
  JOURNAL 
  OF 
  SCIENCE 
  

  

  [FO 
  URTH 
  SERIES.] 
  

  

  Akt. 
  XX. 
  — 
  The 
  Hydrated 
  Ferric 
  Oxides; 
  1 
  by 
  Eugen 
  

   Posnjak 
  and 
  H. 
  E. 
  Merwist. 
  

  

  Contents. 
  

   Introduction. 
  

   Work 
  previously 
  done. 
  

   Analyses. 
  

  

  Discussion 
  of 
  analytical 
  results. 
  

  

  Optical 
  and 
  crystallographie 
  study 
  with 
  synoptic 
  descriptic 
  

   Thermal 
  study. 
  \ 
  fy 
  

  

  Densities 
  of 
  the 
  monohydrates 
  of 
  ferric 
  oxide. 
  \^ 
  

  

  Some 
  observations 
  concerning 
  the 
  relative 
  stability 
  of 
  the 
  hydrated 
  ferric 
  

   oxides. 
  

  

  Synthetic 
  and 
  natural 
  hydrated 
  ferric 
  oxides. 
  

  

  Description 
  of 
  specimens. 
  

  

  Recapitulation. 
  

  

  Introduction. 
  

  

  Our 
  knowledge 
  of 
  the 
  hydrated 
  oxides 
  of 
  iron, 
  notwith- 
  

   standing 
  the 
  extended 
  number 
  of 
  publications 
  on 
  this 
  

   subject, 
  is 
  still 
  very 
  meager. 
  Of 
  the 
  large 
  number 
  of 
  sup- 
  

   posed 
  hydrated 
  oxides 
  to 
  which 
  at 
  one 
  time 
  or 
  another 
  

   definite 
  compositions 
  have 
  been 
  assigned, 
  the 
  text-books 
  

   usually 
  describe 
  the 
  following 
  series 
  as 
  minerals 
  : 
  

  

  Turgite 
  Fe 
  2 
  3 
  -y 
  2 
  H 
  2 
  

  

  Goethite 
  and 
  lepidocrocite 
  Fe 
  2 
  3 
  -H 
  2 
  

  

  Hydrogoethite 
  Fe 
  2 
  3 
  4/3 
  H 
  2 
  

  

  Limonite 
  Fe 
  2 
  3 
  -3/2 
  H 
  2 
  

  

  Xanthosiderite 
  Fe 
  2 
  3 
  -2 
  H 
  2 
  

  

  Limnite 
  Fe 
  2 
  3 
  -3 
  H 
  2 
  

  

  Of 
  these 
  goethite 
  alone 
  has 
  been 
  well 
  defined 
  physically 
  

   and 
  chemically. 
  Descriptions 
  of 
  lepidocrocite 
  (rubin- 
  

   glimmer) 
  leave 
  a 
  doubt 
  as 
  to 
  its 
  identity 
  with 
  goethite, 
  

  

  1 
  This 
  work 
  was 
  begun 
  in 
  connection 
  with 
  the 
  secondary 
  enrichment 
  inves- 
  

   tigation 
  pursued 
  by 
  this 
  Laboratory 
  in 
  1913-1915 
  in 
  co-operation 
  with 
  Pro- 
  

   fessor 
  L. 
  C. 
  Graton 
  and 
  his 
  colleagues. 
  

  

  Am. 
  Jour. 
  Sci. 
  -Fourth 
  Series, 
  Vol. 
  XLVIT, 
  No. 
  281.— 
  May, 
  1919. 
  

   22 
  

  

  