﻿Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  319 
  

  

  Thus 
  a 
  hematite 
  (fibrous) 
  is 
  found 
  to 
  have 
  as 
  much 
  as 
  

   1-3% 
  water; 
  two 
  turgites 
  considerably 
  less 
  water 
  than 
  is 
  

   called 
  for 
  by 
  the 
  formula, 
  while 
  on 
  the 
  other 
  hand 
  goe- 
  

   thites 
  may 
  have 
  too 
  much 
  water. 
  "Limonites" 
  in 
  most 
  

   cases 
  were 
  found 
  to 
  be 
  too 
  low 
  in 
  water 
  for 
  the 
  type 
  of 
  

   hydrate 
  they 
  supposedly 
  represent, 
  as 
  was 
  also 
  the 
  only 
  

   specimen 
  of 
  xanthosiderite 
  which 
  we 
  were 
  able 
  to 
  obtain. 
  15 
  

  

  The 
  ratio 
  of 
  water 
  to 
  ferric 
  oxide 
  for 
  the 
  various 
  

   hydrated 
  ferric 
  oxides 
  is 
  given 
  in 
  Tables 
  I 
  and 
  III. 
  The 
  

   values 
  of 
  this 
  ratio 
  lie 
  between 
  0-1 
  and 
  2-1 
  and 
  embrace, 
  

   therefore, 
  with 
  one 
  exception 
  — 
  Fe 
  2 
  3 
  -3H 
  2 
  — 
  all 
  the 
  sup- 
  

   posed 
  hydrated 
  ferric 
  oxides 
  usually 
  described 
  as 
  min- 
  

   erals, 
  and 
  mentioned 
  in 
  the 
  beginning 
  of 
  this 
  paper. 
  

   However, 
  this 
  ratio 
  shows 
  practically 
  a 
  continuous 
  varia- 
  

   tion 
  instead 
  of 
  sudden 
  changes 
  as 
  should 
  be 
  expected 
  for 
  

   a 
  Series 
  of 
  hydrates. 
  It 
  was 
  rather 
  surprising 
  to 
  find 
  

   that 
  the 
  limited 
  number 
  of 
  specimens 
  which 
  we 
  analyzed 
  

   presented 
  such 
  a 
  gradation, 
  as 
  the 
  selection 
  of 
  specimens 
  

   for 
  the 
  analyses 
  in 
  Table 
  I 
  was 
  made 
  entirely 
  on 
  the 
  basis 
  

   of 
  optical 
  homogeneity 
  and 
  optical 
  differences. 
  

  

  It 
  may 
  further 
  be 
  stated 
  in 
  respect 
  to 
  these 
  analyses, 
  

   that 
  probably 
  not 
  all 
  of 
  the 
  water 
  determined 
  in 
  these 
  

   substances 
  belongs 
  to 
  the 
  hydrated 
  ferric 
  oxide, 
  but 
  that 
  

   some 
  of 
  it 
  belongs 
  to 
  the 
  " 
  impurities,'' 
  chief 
  among 
  

   which 
  is 
  silica. 
  Usually 
  the 
  water 
  content 
  is 
  higher 
  the 
  

   larger 
  the 
  amount 
  of 
  such 
  impurities 
  (see 
  Tables 
  I 
  and 
  

   III). 
  The 
  ratios 
  of 
  water 
  to 
  ferric 
  oxide 
  given 
  in 
  Tables 
  

   I 
  and 
  II 
  are, 
  therefore, 
  somewhat 
  too 
  high 
  to 
  be 
  repre- 
  

   sentative 
  because 
  the 
  total 
  amount 
  of 
  water 
  was 
  taken. 
  

   It 
  is 
  noteworthy 
  that 
  even 
  after 
  this 
  fact 
  has 
  been 
  taken 
  

   into 
  account, 
  the 
  respective 
  ratios 
  of 
  most 
  "limonites" 
  

   and 
  turgites 
  are 
  not 
  sufficiently 
  high 
  for 
  the 
  hydrates 
  they 
  

   supposedly 
  represent. 
  It 
  seems, 
  therefore, 
  that 
  on 
  the 
  

   basis 
  of 
  analytical 
  data 
  there 
  is 
  little 
  foundation 
  for 
  the 
  

   series 
  of 
  hydrates 
  of 
  ferric 
  oxide, 
  which 
  is 
  commonly 
  

   assumed. 
  

  

  Optical 
  and 
  Crystallographic 
  Study, 
  with 
  Synoptic 
  Descriptions. 
  

  

  In 
  order 
  that 
  the 
  terms 
  used 
  in 
  the 
  latter 
  part 
  of 
  the 
  

   paper 
  may 
  have 
  as 
  definite 
  a 
  significance 
  as 
  can 
  be 
  given 
  

   before 
  those 
  parts 
  of 
  the 
  paper 
  have 
  been 
  read, 
  short 
  

   descriptions 
  including 
  microscopical 
  characteristics 
  will 
  

   be 
  given 
  at 
  once. 
  

  

  15 
  Fischer, 
  loc. 
  cit., 
  makes 
  similar 
  statements 
  in 
  respect 
  to 
  the 
  last 
  two 
  

   minerals. 
  

  

  