﻿Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  339 
  

  

  hydrates 
  to 
  be 
  truly 
  stable 
  under 
  any 
  given 
  set 
  of 
  condi- 
  

   tions. 
  The 
  evidence 
  presented 
  in 
  this 
  paper 
  as 
  to 
  the 
  

   existence 
  of 
  only 
  ferric 
  oxide 
  nionohydrate 
  and 
  a 
  solid 
  

   solution 
  of 
  this 
  substance 
  and 
  ferric 
  oxide, 
  however, 
  dis- 
  

   poses 
  of 
  the 
  assumed 
  series 
  of 
  ferric 
  oxide 
  hydrates. 
  

   The 
  dehydration 
  experiments 
  further 
  indicate 
  that 
  ferric 
  

   oxide 
  nionohydrate 
  is 
  probably 
  stable 
  at 
  any 
  temperature 
  

   which 
  the 
  earth's 
  surface 
  may 
  normally 
  reach 
  and 
  it 
  is 
  

   therefore 
  unlikely 
  that 
  in 
  nature 
  the 
  red 
  ferric 
  oxide 
  is 
  

   derived 
  by 
  the 
  direct 
  dehydration 
  of 
  the 
  yellow. 
  It 
  is 
  

   probable 
  that 
  both 
  red 
  and 
  yellow 
  substances 
  may 
  be 
  

   formed 
  at 
  ordinary 
  temperatures 
  by 
  somewhat 
  different 
  

   chemical 
  reactions 
  ; 
  both 
  are 
  relatively 
  stable 
  under 
  the 
  

   conditions 
  usually 
  met 
  with 
  near 
  the 
  earth's 
  surface. 
  No 
  

   definite 
  statement 
  concerning* 
  their 
  stability 
  relation 
  can 
  

   be 
  made 
  at 
  present 
  and 
  further 
  studies 
  are 
  required 
  for 
  

   the 
  solution 
  of 
  this 
  problem. 
  4S 
  

  

  Synthetic 
  and 
  Natural 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  As 
  was 
  previously 
  mentioned, 
  statements 
  concerning 
  

   the 
  formation 
  of 
  definite 
  crystallized 
  hydrates 
  were 
  rein- 
  

   vestigated 
  by 
  van 
  Bemmelen 
  49 
  and 
  proved 
  by 
  him 
  to 
  be 
  

   erroneous. 
  The 
  supposed 
  crystals 
  prepared 
  by 
  himself 
  

   were 
  undoubtedly 
  pseudomorphs 
  after 
  sodium-f 
  errite 
  and 
  

   it 
  seems 
  certain 
  that 
  up 
  to 
  the 
  present 
  no 
  synthesis 
  of 
  

   definitely 
  crystallized 
  hydrated 
  ferric 
  oxide 
  has 
  been 
  sue- 
  

  

  +s 
  As 
  mentioned 
  in 
  the 
  beginning 
  of 
  this 
  paper, 
  attempts 
  were 
  made 
  to 
  form 
  

   crystallized 
  hydrated 
  ferric 
  oxides. 
  Various 
  reactions 
  were 
  tried 
  but 
  only 
  

   "amorphous" 
  red 
  and 
  yellow 
  substances 
  were 
  obtained; 
  finally 
  the 
  system 
  

   Fe 
  : 
  3 
  -S0 
  3 
  -H 
  2 
  was 
  systematically 
  studied. 
  A 
  paper 
  dealing 
  -with 
  this 
  system 
  

   will 
  soon 
  be 
  published. 
  While 
  this 
  study 
  did 
  not 
  yield 
  all 
  the 
  information 
  

   that 
  was 
  desired 
  it 
  may 
  be 
  of 
  interest 
  here 
  to 
  mention 
  a 
  few 
  of 
  the 
  results 
  

   obtained. 
  Yellow 
  hydrated 
  ferric 
  oxide, 
  resembling 
  in 
  its 
  optical 
  and 
  

   thermal 
  behavior 
  (see 
  fig. 
  1, 
  No. 
  24) 
  the 
  natural 
  "amorphous" 
  hydrated 
  

   ferric 
  oxide, 
  was 
  formed 
  below 
  approximately 
  120°, 
  while 
  only 
  above 
  that 
  

   temperature 
  were 
  red 
  hydrated 
  ferric 
  oxide, 
  resembling 
  turgite, 
  and 
  hema- 
  

   tite 
  formed. 
  The 
  temperature 
  given 
  may 
  not 
  be 
  exact, 
  as 
  it 
  was 
  not 
  possible 
  

   on 
  account 
  of 
  slow 
  reaction 
  to 
  establish 
  equilibrium 
  from 
  both 
  sides; 
  how- 
  

   ever, 
  it 
  seems 
  certain 
  that 
  at 
  lower 
  temperatures 
  only 
  the 
  yellow 
  substance 
  

   is 
  stable 
  under 
  such 
  conditions. 
  Most 
  of 
  the 
  hydrated 
  ferric 
  oxides 
  thus 
  

   formed 
  contained 
  considerable 
  amounts 
  of 
  sulphate, 
  which 
  varied 
  with 
  the 
  

   concentration 
  of 
  the 
  solution 
  and 
  temperature 
  and 
  was 
  proven 
  to 
  be 
  adsorbed 
  

   and 
  not 
  due 
  to 
  presence 
  of 
  ferric 
  sulphates. 
  The 
  strong 
  adsorptive 
  power 
  

   of 
  the 
  hydrated 
  ferric 
  oxides 
  — 
  (Biltz, 
  Ber. 
  37, 
  3138, 
  1904 
  has 
  shown 
  that 
  

   an 
  adsorption 
  phenomenon 
  is 
  responsible 
  for 
  its 
  use, 
  proposed 
  by 
  Bunsen, 
  as 
  

   an 
  antidote 
  for 
  arsenic 
  poisoning) 
  — 
  is 
  probably 
  one 
  of 
  the 
  chief 
  causes 
  

   impeding 
  the 
  formation 
  of 
  crystallized 
  products: 
  the 
  surfaces 
  of 
  the 
  newly- 
  

   formed 
  nuclei 
  becoming: 
  saturated 
  due 
  to 
  adsorption. 
  Another 
  cause 
  is 
  the 
  

   extremely 
  small 
  solubility 
  of 
  hydrated 
  ferric 
  oxide 
  in 
  pure 
  water. 
  

  

  49 
  Loc. 
  eit. 
  

  

  