﻿334 
  Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  describe 
  properties 
  caused 
  by 
  some 
  general 
  physical 
  con- 
  

   dition) 
  it 
  is 
  still 
  possible 
  that 
  * 
  ' 
  limonite 
  ' 
  ' 
  could 
  also 
  be 
  

   a 
  distinct 
  polymorphic 
  form 
  of 
  ferric 
  oxide 
  monohydrate. 
  

   To 
  decide 
  this 
  question 
  some 
  further 
  study 
  was 
  necessary 
  

   (density, 
  optical 
  properties, 
  etc.). 
  

  

  Densities 
  of 
  the 
  Monohydrates 
  of 
  Ferric 
  Oxide. 
  

  

  Information 
  about 
  the 
  number 
  of 
  polymorphic 
  mono- 
  

   hydrates 
  of 
  ferric 
  oxide 
  in 
  existence 
  was 
  sought 
  by 
  means 
  

   of 
  density 
  determinations. 
  Available 
  data 
  for 
  the 
  sup- 
  

   posed 
  hydrates 
  show 
  considerable 
  but 
  irregular 
  differ- 
  

   ences. 
  Thus 
  Dana 
  gives 
  in 
  his 
  "System 
  of 
  Mineralogy" 
  

   the 
  density 
  of 
  goethite 
  (and 
  lepidocrocite) 
  as 
  4-0-44 
  and 
  

   the 
  density 
  of 
  limonite 
  as 
  3-6-4-0. 
  The 
  density 
  of 
  hydro- 
  

   goethite 
  is 
  given 
  by 
  Zemjatschensky 
  and 
  SamojlofT 
  as 
  

   3-5-3-7. 
  

  

  In 
  view 
  of 
  the 
  fibrous 
  character 
  of 
  many 
  of 
  our 
  speci- 
  

   mens 
  great 
  care 
  had 
  to 
  be 
  taken, 
  in 
  determining 
  this 
  con- 
  

   stant 
  accurately, 
  to 
  drive 
  out 
  all 
  the 
  air. 
  The 
  substance 
  

   to 
  be 
  examined 
  passed 
  a 
  100 
  mesh 
  and 
  was 
  held 
  by 
  a 
  200 
  

   mesh 
  (per 
  linear 
  inch) 
  sieve. 
  The 
  pycnometer 
  described 
  

   by 
  J. 
  Johnston 
  and 
  L. 
  H. 
  Adams 
  43 
  for 
  specific 
  gravity 
  

   determination 
  was 
  used 
  and 
  the 
  air 
  carefully 
  boiled 
  out 
  

   under 
  reduced 
  pressure. 
  Repeated 
  determinations 
  were 
  

   in 
  good 
  agreement 
  differing 
  only 
  in 
  the 
  third 
  decimal. 
  

   Comparative 
  density 
  determinations 
  in 
  xylol 
  to 
  determine 
  

   whether 
  complete 
  filling 
  of 
  pores 
  took 
  place 
  in 
  our 
  experi- 
  

   ments 
  were 
  also 
  attempted. 
  However, 
  only 
  in 
  cases 
  

   where 
  little 
  excess 
  water 
  was 
  present 
  were 
  these 
  deter- 
  

   minations 
  successful 
  and 
  the 
  values 
  then 
  obtained 
  were 
  

   identical 
  with 
  those 
  in 
  water. 
  Where 
  more 
  water 
  was 
  

   present 
  some 
  was 
  easily 
  liberated 
  in 
  boiling 
  out 
  the 
  air 
  

   and 
  small 
  drops 
  of 
  it 
  were 
  observed 
  in 
  the 
  xylol. 
  The 
  

   values 
  for 
  the 
  specific 
  gravity 
  were 
  accordingly 
  consider- 
  

   ably 
  lower 
  than 
  in 
  water 
  and 
  the 
  latter 
  probably 
  essen- 
  

   tially 
  correct. 
  

  

  The 
  specific 
  gravities 
  given 
  in 
  Table 
  VI 
  show 
  the 
  wide 
  

   variation 
  usually 
  found 
  in 
  these 
  substances. 
  However, 
  

   we 
  know 
  from 
  the 
  analyses 
  that 
  they 
  contain 
  a 
  consider- 
  

   able 
  amount 
  of 
  impurities 
  and 
  the 
  result 
  is 
  therefore 
  

   not 
  surprising. 
  Comparison 
  of 
  these 
  data 
  is 
  possible 
  

   only 
  after 
  the 
  proper 
  corrections 
  are 
  made 
  for 
  these 
  

   impurities. 
  

  

  43 
  J. 
  Am. 
  Chem. 
  Soc. 
  34, 
  563 
  (1912). 
  

  

  